Aqueous polymer compositions

ABSTRACT

Aqueous polymer composition suitable for coating which comprises the following components dispersed in water: (1) a combination of an acrylic polymer(s) A and an acrylic polymer(s) B where polymer(s) A has a Tg of not more than 30° C. and polymer(s) B has a Tg of at least 35° C., more preferably at least 45° C., which is at least 25° C. higher than the Tg of polymer(s) A, and wherein one or both of polymers A and B bear crosslinker functional groups capable of imparting ambient-temperature crosslinkability to component (1) in a coating formed from the composition via the formation of non-radically-formed covalent bonds; and (2) a self-dispersible, ionically stabilised polymer having olefinically unsaturated bond functionality capable of imparting radiation-curability (preferably uv-radiation curability) thereto in a coating formed from the composition.

The present invention relates to certain dual-cure polymer compositions,their use in coating, and coatings derived therefrom.

There is an ongoing demand to provide aqueous polymer compositionssuitable for coatings which have an excellent balance of properties,such as for example good dispersion stability of the components of thecompositions, good chemical and solvent resistance of coatings formedfrom the compositions, and a combination of facile film formation (i.e.low minimum film forming temperature MFT, preferably ambient temperatureor below) as well as good hardness and blocking resistance in coatingsformed from the composition at low or no coalescent aid requirement inthe composition (these being organic solvents or plasticisers whichassist film formation but may be undesirable for environmental reasons).

We have now discovered certain aqueous compositions having such anexcellent balance of properties as mentioned above.

According to the present invention there is provided an aqueous polymercomposition suitable for coating which comprises the followingcomponents dispersed in water:

(1) a combination of an acrylic polymer(s) A and an acrylic polymer(s) Bwhere polymer(s) A has a Tg of not more than 30° C. and polymer(s) B hasa Tg of at least 35° C., more preferably at least 45° C., which is atleast 25° C. higher than the Tg of polymer A, and wherein one or both ofpolymers A and B bear crosslinker functional groups capable of impartingambient-temperature crosslinkability to component (1) in a coatingformed from the composition via the formation of non-radically-formedcovalent bonds; and

(2) a self-dispersible, ionically stabilised polymer having olefinicallyunsaturated bond functionality capable of imparting radiation-curabilitythereto in a coating formed from the composition.

There is also provided according to the invention a method of coating asubstrate using an aqueous polymer composition as defined above.

There is further provided according to the invention a coatingobtainable or derived from an aqueous composition as defined above.

There is further provided according to the invention a substrate havinga coating obtainable or derived from an aqueous composition as definedabove.

Aqueous polymer dispersions for coatings which comprise two polymers ofdiffering Tg, one having a Tg of not more than 10° C. and the otherhaving a Tg>25° C., and also a multi functional material having at leasttwo ethylenically unsaturated groups which can each participate in afree-radical initiated addition polymerisation, are known fromEP-A-0736573. The dispersions are said to be curable by heat orradiation. In addition, the polymers of differing Tg may bear groups forgrafting or crosslinking purposes, although these are not employed inthe worked examples. The multifunctional material is said at page 4lines 30 to 32 to be either not emulsified or emulsified in the water ofthe polymer dispersion, and in the latter case it may be emulsified withthe aid of surfactants such as those used in aqueous emulsionpolymerisation. While it is further stated at page 4 lines 7 to 12 thatthe multifunctional compounds may incorporate internal hydrophiliccomponents to facilitate such emulsification (although this is notexemplified in a worked example), the earlier-stated requirement to alsoemploy external surfactant when emulsification is required is not saidto be negated, so the multi-functional compound of EP-A-0736573 evenwhen containing internal hydrophilic components is not self-dispersibleas defined in this specification (see later). We have found that theaqueous compositions of the present invention surprisingly provideimproved properties in comparison to the type of composition taught inEP-A-0736573, and in particular improved resistance to blocking ofcoatings made from the compositions, both before and after radiationcuring, and improved dispersion stability.

For the purposes of this invention, by an “aqueous polymer composition”is meant a dispersion of polymers of components (1) and (2) in a liquidcarrier medium of which water is the principal component (at least 50weight %, more usually at least 80 weight %). Minor amounts of organicliquids may optionally be present although it is preferred that theaqueous composition is substantially solvent-free, by which is meantthat the composition contains less than 5 wt % of organic solvent(s)based on total polymer solids, more preferably less than 2 wt %, andmost preferably no solvent at all. (In this specification organicplasticisers are intended to be within the scope of the term “solvent”;these, like coalescent solvents, are also used in the art to decreaseMFT although strictly speaking they are not solvents).

The invention composition will typically comprise colloidally dispersedparticles of the polymers of components (1) and (2), i.e. will typicallybe in the form of an aqueous polymer latex.

The MFT of the invention composition is preferably less than 35° C., andis particular ambient temperature or below. By ambient temperature ismeant herein a temperature within the range 10 to 25° C.

The crosslinker functional groups of the acrylic polymer(s) of component(1) are usually chain-pendant and/or terminal. The groups on the polymerof component (2), which provide radiation curability are olefinicallyunsaturated bonds and are usually chain-pendant and/or terminal, but mayalso be in-chain.

The aqueous invention composition may be termed a “dual-cure”composition because the polymers of components (1) and (2) arecrosslinkable, after forming a film from the composition, by differentcrosslinking mechanisms, as will now be explained (although, as willalso be explained, in some embodiments of the invention, the polymer ofcomponent (2) takes part in the crosslinking of the polymer(s) ofcomponent (1) as well as crosslinking by a different crosslinkingmechanism).

In component (1), one or both of acrylic polymers A and B bearcrosslinker functional groups, i.e. groups which can impartambient-temperature crosslinkability to this component via the formationof non-radically-formed covalent bonds, by which we mean herein covalentbonds which are formed other than by a free-radical addition mechanism(auto-oxidation being considered as forming bonds by a free radicalmechanism for the purposes of this invention, ie such bond formationbeing excluded from the scope of the invention) or by an anionic orcationic addition polymerisation mechanism. (However, crosslinking bycoordinate bond formation as e.g. by lone electron pair donation fromgroups such as carboxyl groups (oxygen atoms thereof) to acceptor shellsof metal ions of appropriate metal compounds is intended to be withinthe scope of the term non-radically-formed covalent bonds). To form suchbonds, such crosslinker groups must undergo reaction with other groupsborne by compounds already present in the composition or which aresubsequently added thereto. (In the case of coordinate bond formationthe lone pair of atoms of crosslinker groups coordinate to acceptormetal ion shells of already present or subsequently added metalcompounds).

In the most preferred embodiment of the invention (embodiment X forfuture reference), one or both of polymers A and B carry crosslinkergroups and the composition contains, or is subsequently mixed with, anexternal crosslinking agent having 2 or more groups (or in the case ofcoordinate bond formation, an acceptor metal ion shell—see eg EP-A-6547and U.S. Pat. No. 2,904,526) which are reactable with the crosslinkergroups on polymers A and/or B to form the crosslinking covalent bonds.By “external” is meant that the crosslinking agent is exclusive of thepolymers of components (1) and (2) (i.e. is not provided by any of thesepolymers).

For the achievement of ambient-temperature crosslinkability inembodiment X it is preferred that the crosslinker groups on the polymersA and/or B are carbonyl groups (by which is meant, unless otherwisespecified, the carbonyl functionality of a ketone or aldehyde group),and the groups reactive therewith of the external crosslinking agent arecarbonyl-reactive amino groups, with the converse situation also inprinciple being feasible (i.e. carbonyl-reactive amino groups on thepolymers A and/or B and carbonyl groups on the external crosslinkingagent) but less preferred.

By an amino group is meant herein a carbonyl reactive group of theformula —NH₂ or —NH—, or a carbonyl-reactive group derived therefrom,and for the purposes of this invention is intended to embrace groups offormula —NHNHR¹ (where R¹ is H or lower alkyl of 1-5 carbon atoms,preferably methyl), more commonly known as hydrazine functional groups,or carbonyl-reactive hydrazone groups derived therefrom (when R¹ is H),as well as —NH₂ or —NH— groups which are bound only to a carbon atom(s)(i.e. conventional primary or secondary amine groups), orcarbonyl-reactive groups derived therefrom (e.g. by reaction with aketone of three or more carbon atoms). The amino group could also bebound to an oxygen atom.

Hydrazine functional groups are often part of larger groups such as acidhydrazide groups and semi-carbazide groups.

Another possibility for embodiment X is that the crosslinker groups onthe polymers A and/or B are carboxyl groups and the groups reactivetherewith of the external crosslinking agent are aziridine groups (acyclic —NH— containing group), with the converse situation also inprinciple being feasible (i.e. aziridine groups on the polymers A and/orB and carboxyl groups on the external crosslinking agent) but lesspreferred.

A further possibility for embodiment X (as indicated above) is that lonepairs of electrons of oxygen atoms of carboxyl groups on polymers Aand/or B (the crosslinker groups) form coordinate covalent crosslinkingbonds on coating formation by donation to acceptor metal ion shells ofan added metal compound (the external crosslinking agent) such as zinccations added as zinc oxide. (The lone pair of an oxygen atom of acarboxyl group is thought to be delocalised between the two oxygen atomsof the group, so that bidentate coordinate bonding to a zinc cation isthought to occur on coating formation.)

The above examples given for effecting crosslinking in embodiment X arenot intended to be limiting and a more comprehensive list for thepossible groups on polymers A and/or B (on the one hand) and theexternal crosslinking agent (on the other) is as follows: ketone(nonenolic) and polyhydrazide; ketone(non enolic) and polyamine;acetoacetoxy and polyhydrazide; acetoacetoxy and polyamine; silane andpolysilane; hydroxyl and polyisocyanate (optionally blocked); hydroxyland melamine; carboxyl and polyepoxy; epoxy and polycarboxyl; carboxyland carbodiimide; amine and polyepoxy; carboxyl and metal ion (forcoordinate bonding); carboxyl and polyaziridine; carboxyl andepoxysilane; amine and epoxysilane.

Specific examples of methods for incorporating crosslinker groups onpolymers A and/or B and specific examples of crosslinking agents will begiven later in this specification.

In another embodiment of the invention (embodiment Y for futurereference), each polymer A and B carries different crosslinker groupswhich are reactable with each other (co-reactable) to form the covalentbonds leading to crosslinking. In this embodiment, therefore, there isno requirement for the presence of an external crosslinking agent,although one may still be present if desired (providing groups whichreact with the crosslinker groups on polymers A and/or B). The different(co-reactable) crosslinker groups borne by polymers A and B will usuallybe restricted to be being carried only on one or other of the polymers Aand B, i.e. polymer A will carry only one of two types of co-reactivegroup, while polymer B will carry only the other type of co-reactivegroups. However, it is feasible in this embodiment for one or both ofpolymers A and B to carry both types of co-reactive groups.

For the achievement of ambient temperature crosslinkability in thisembodiment, it is preferred that the co-reactive crosslinker groups are,respectively, carbonyl groups and carbonyl-reactive amino groups, orsilane and hydroxyl groups. The nature of the carbonyl reactive aminogroups has been discussed in the embodiment X detailed above; howevertypically they are provided by pendant amino ester groups which may beformed by imination of a precursor carboxyl functional polymers (seebelow the discussion of embodiment Z for a fuller discussion of this).

It may be mentioned that carbonyl groups and carbonyl reactive aminogroups are believed to react with each other to form azomethine groupsor possibly enamine groups in the case when the carbonyl group is anenolic carbonyl group (as e.g. in an acetoacetate group). However we donot wish to be bound by these views regarding the specific type ofcovalent bond formation between the carbonyl and amino groups.

The above examples for achieving crosslinking in embodiment Y is notintended to be limiting, and a more comprehensive list for the possibleco-reactive groups on polymers A and B in this embodiment is as follows:silane and hydroxyl; acetoacetoxy and and amine; ketone(non enolic) andamine; acetoacetoxy and hydrazide; ketone(non enolic) and hydrazide;carboxyl and epoxy; hydroxyl and isocyanate (optionally blocked);hydroxyl and methylol(meth)acrylamide. It may be mentioned that thepolymer of component (2) could optionally bear one or other of theco-reactive crosslinker groups.

In a further embodiment of the invention (embodiment Z for futurereference) one or both of the acrylic polymers A and B carry crosslinkergroups of the type which are reactable with the groups on the polymer ofcomponent (2) which impart radiation curability thereto—i.e.olefinically unsaturated bonds. In effect, some of the polymer ofcomponent (2) acts as an internal crosslinking agent for the reactionwith the crosslinker groups on one or both of polymers A and B, with theremainder providing the radiation—curability of the polymer composition.

In this embodiment it is preferred that the crosslinker groups on one orboth of the polymers A and B are primary or secondary amine groups whichhave been discussed above in relation to the other embodiments X and Y,while the groups reactable therewith on the polymer of component (2) areolefinically unsaturated bonds (preferably being provided by acryloyl,fumaric or maleic groups) with covalent bond formation being effected byMichael addition of the amino groups to the unsaturated bonds. Theprovision of amine groups on the acrylic polymer(s) of component (1) mayfor example be effected by reacting a precursor polymer bearing chainpendant carboxyl groups with an alkylene imine (particularly ethyleneimine or propylene imine) to form (from the carboxyl groups) pendantamino ester groups which are terminated by primary amine groups; thisreaction is commonly called an imination reaction, with the so formedacrylic polymer being termed herein an iminated acrylic polymer.

The above mentioned possibility for the crosslinker groups on one orboth of polymers A and/or B in embodiment Z is not intended to belimiting, and such groups could eg also be mercaptane groups oracetoacetoxy groups.

In yet a further embodiment of the invention (embodiment Q for futurereference) one or both of the acrylic polymers A and B of component (1)carry crosslinker groups, and the radiation curable polymer of component(2) also carries crosslinker groups (preferably the same as those ofpolymer A and/or B of component (1)), these not being the olefinicallyunsaturated groups which impart radiation curability to the polymer ofcomponent (2), and the composition contains, or is subsequently mixedwith, an external crosslinking agent having 2 or more groups (or acrosslinking metal ion for coordinate bond formation) which arereactable with the crosslinker groups on polymers A and/or B and on thepolymer of component (2) to form the crosslinking covalent bonds. Inthis embodiment the non-radical covalent crosslinking of component (1)does not affect the unsaturated double bonds of the polymer of component(2).

In embodiment Q, the crosslinker groups on polymer A and/or polymer B ofcomponent (1) and the crosslinker groups on the polymer of component (2)(for reacting with an external crosslinking agent) are usefully carboxylgroups, and the groups reactive therewith of the external crosslinkingagent are usefully aziridine groups. Another useful crosslinking systemfor embodiment Q has carboxyl groups on one or both of acrylic polymersA and B and on the polymer of component (2), and metal ions from anexternal crosslinking agent (for coordinate bond formation).

In an alternative version of embodiment Q, one or both of the acrylicpolymers A and B of component (1) on the one hand bear crosslinkergroups and the polymer of component (2) on the other hand bearsco-reactive crosslinker groups (these not being the olefinicallyunsaturated groups for imparting radiation curability to polymer (2)).For example one both acrylic polymers could bear carbonyl groups and thepolymer of component (2) could bear hydrazide or semicarbazide groups(if polymer (2) was a polyurethane—see later—these groups could eg beintroduced by overextension of an isocyanate terminated urethaneprepolymer). In this version of embodiment Q, an external crosslinkingagent is not required (but may be present if desired).

The above possibilities given for achieving crosslinking in embodiment Qis not intended to be limiting. A more comprehensive list (whereexternal crosslinking agent is required) for possible groups on polymersA and/or B and on polymer of component (2), on the one hand, and on anexternal crosslinking agent on the other, is as follows: carboxyl andmetal ion; carboxyl and aziridine; carboxyl and carbodiimide; carboxyland (poly)epoxy; hydroxyl and isocyanate (optionally blocked); hydroxyland melamine; hydroxyl and silane; hydroxyl andmethylol(meth)acrylamide; ketone(non enolic) and hydrazide; ketone(nonenolic) and amine; acetoacetoxy and hydrazide; acetoacetoxy and amine;silane and silane; epoxy and amine; epoxy and mercaptane. Note that thegroups on A and B (if both bear them) are not necessarily the same. Inthe alternative version of embodiment Q (not requiring externalcrosslinking agent), the groups on polymers A and/or B on the one hand,and on the polymer of polymer (2) on the other, could be: ketone(nonenolic) and hydrazide; acetoacetoxy and hydrazide.

It will be appreciated that one or more of the embodiments X, Y, Z and Qcould be operative at the same time in the invention composition.

The radiation-curability of the polymer of component (2) results (asmentioned above) from the presence of olefinically unsaturated bonds,and takes place by a free-radical mechanism. Such bonds may e.g. becontained in (meth)acryloyl groups pendant or chain terminal to thepolymer chain.

The radiation used for crosslinking (i.e. curing) the polymer ofcomponent (2), after drying, may be provided by any suitable form ofradiant energy, but is preferably ultra-violet (uv) radiation. Inprinciple, electron-beam (eb) radiation or (in some cases) visibleradiation could be used. When crosslinking is effected by uv radiation(or visible radiation), the composition will normally include at leastone photoinitiator (or sensitizer), usually present in an amount 0.1 to10% by weight, based on the solid polymer weight of component (2).Examples of uv photoinitiators include halogenated polynuclear ketonessuch as chlorosulphonated benzanthones, chlorosulphonated fluorenones,alpha-haloalkylated benzanthones, alpha-haloalkylated fluorenones andalkyl phenones. Accelerator compounds may be included if desired toenhance the cure rate. (When curing is to be effected by eb radiation,photoinitiator is not required).

After the invention composition has been applied to a substrate to forma coating, and before, during and/or after drying the applied wet film,usually during and/or after drying (drying often being effected, atambient temperature, although this may be accelerated if desired by theapplication of heat) crosslinking occurs at ambient temperature in thepolymer component (1), although the crosslinking rate may be acceleratedif desired by heating at an elevated temperature. Radiation crosslinkingof the polymer of component (2) will occur when the coating is subjectedto suitable radiation, and, again this can be done before, during and/orafter drying the applied wet film (usually shortly after drying). Toeffect the radiation curing of component (2), the aqueous phase of a wetfilm of the composition is sometimes flashed off quickly (at an elevatedtemperature) to dry the composition before applying radiation at ambient(or a higher) temperature. Curing by radiation will take place far morerapidly than curing by non-radically-formed covalent bond formation.

Turning more specifically to the acrylic polymers A and B of component(1). An acrylic polymer(s) A having a Tg of not more than 30° C. istermed herein a “soft” polymer for convenience, while an acrylicpolymer(s) B having a Tg of at least 35° C. (more preferably at least45° C.) is termed herein a “hard” polymer for convenience. Preferably asoft acrylic polymer has a Tg within the range of from −60 to 30° C.,more preferably from −20 to 15° C., and a hard acrylic polymerpreferably has a Tg within the range of from 35 to 125° C., morepreferably 45 to 125° C., and still more preferably 50 to 100° C. The Tgof the hard polymer should be at least 25° C. higher than that of thesoft polymer, more preferably at least 40° C. higher, and especiallypreferably at least 50° C. higher. The weight ratio of soft to hardacrylic polymers is preferably within the range of from 30/70 to 90/10,more preferably from 40/60 to 80/20.

The acrylic polymers of differing Tg (as defined) may be present in thecomposition as a single blend of preformed (separately prepared)polymers, or, more preferably, as a sequentially-formed composition ofthe polymers, whereby one acrylic polymer has been prepared (bypolymerisation of its constituent monomers) in the presence of another,preformed, acrylic polymer (possibly, but not necessarily, resulting inthe acrylic polymers being in a core/shell particle arrangement), againso that there is a Tg difference (as defined) between the acrylicpolymers.

In embodiment X of the invention, the amount of crosslinker groups(present on one or both of polymers A and B) preferably corresponds to apresence of such groups in the range of up to 1.25 mmoles of suchgroups/g of the polymers A and B combined, more preferably up to 1.0mmoles of such groups/g of polymers A and B combined, most preferred upto 0.6 mmoles of such groups/g of polymers A and B combined. The amountof external crosslinking agent preferably corresponds to the followingstoichiometric amounts: 0.05 to 1.5 SA (ratio of equivalents ofcomponent (1) crosslinker groups to equivalents of external crosslinkercrosslinking groups, or in the case of coordinate bond formation, toequivalents of acceptor metal ion), more preferably 0.1 to 1.0 SA.

In embodiment Y of the invention, the amount of each co-reactive type ofcrosslinker group preferably each corresponds to a presence of suchgroups in the range of up to 1.0 mmoles of such groups/g of the polymersA and B combined, more preferably up to 0.8 mmoles of such groups/g ofpolymers A and B combined.

In embodiment Z of the invention, the amount of crosslinker groups onone or both polymers A and B preferably corresponds to a presence ofsuch groups in the range of up to 1.0 mmoles of such groups/g of thepolymers A and B combined, more preferably up to 0.8 mmoles of suchgroups/g of polymers A and B combined.

In embodiment Q of the invention (where external crosslinker isrequired), the amount of the non radical covalent bond-providingcrosslinker groups present on one or both of polymers A and B and on thepolymer of component (2) preferably corresponds to a presence of suchgroups in the range of 0.05 to 2.0 mmoles of such groups/g of polymersA, B and the polymer of component (2) combined, more preferably 0.1 to1.5 mmoles of such groups/g and most preferred 0.2 to 0.9 mmoles of suchgroups. The amount of external crosslinking agent preferably correspondsto 0.05 to 1.5 SA (ratio of equivalents of crosslinker groups oncomponent (1) and component (2) polymers to equivalents of externalcrosslinker crosslinking groups), more preferably 0.1 to 1.0 SA.

By an acrylic polymer herein is meant a homo- or copolymer derived fromthe addition polymerisation (using a free radical initiated process andusually in an aqueous medium) of a monomer composition comprising atleast 40 weight % of one or more monomers of the formula

CH₂═CR²COOR³  1

where R² is H or methyl, and R³ is optionally substituted alkyl of 1 to20 carbon atoms (more preferably 1 to 9 carbon atoms) or cycloalkyl of 5to 20 carbon atoms. Such monomers are referred to herein as acrylicmonomers. More preferably, the monomer composition contains at least 50weight % of acrylic monomer(s), and particularly at least 60 weight %.Examples of such acrylic monomers include methyl acrylate, methylmethacrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate,iso-butyl acrylate, n-butyl methacrylate, iso-butyl methacrylate,2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, isopropyl acrylate,isopropyl methacrylate, n-propyl acrylate, n-propyl methacrylate,dodecyl methacrylate, dodecyl acrylate, stearyl methacrylate and stearylacrylate.

One or both of the soft acrylic polymer A and the hard acrylic polymer Bmust of course contain crosslinker functional groups, and these arepreferably derived from olefinically unsaturated monomers employed inthe polymerisation bearing a required crosslinker group(s) (crosslinkermonomers for convenience), or a precursor group(s) which is subsequentlyconverted to a crosslinker functional group(s) after polymerisation.

In embodiment X, the crosslinker functional groups could be eg carbonylgroups, and crosslinker monomers for providing such groups are suitablynon enolic keto and aldehyde functional monomers such as acrolein,methacrolein, methyl vinyl ketone, and diacetone acrylamide, and enoliccarbonyl monomers such as the acetoacetoxy esters of hydroxyalkyl(usually C1 to C12) acrylates and methacrylates, examples of which areacetoacetoxyethyl methacrylate and acrylate, and acetoacetoamidoethylmethacrylate. Other possible crosslinker groups include carboxyl groups,and crosslinker monomers for providing such groups include olefinicallyunsaturated mono or dicarboxylic acids such as acrylic acid, methacrylicacid, 2-carboxyethyl acrylate, fumaric acid, maleic acid, and itaconicacid.

In embodiment Y, the co-reactive crosslinker functional groups could beeg carbonyl and amino (as discussed above), and the carbonyl groups arepreferably provided by using keto and aldehyde functional monomers asdiscussed above (examples of such monomers being given above); aminocrosslinker groups are preferably provided by employing carboxylicacid-functional monomers in the polymerisation and subsequentlyiminating the acrylic polymer to form pendant amino crosslinker groups(as discussed above). Also hydrazinolysis can be employed to make thepolymer amine functional. In embodiment Z (discussed above), thecrosslinker functional groups could also be eg amino groups, and arelikewise usefully obtainable by subsequent imination of carboxyl groupsintroduced by using a carboxylic acid functional monomer in the acrylicpolymerisation.

The monomer composition to form an acrylic polymer may also include anolefinically unsaturated monomer(s) other than the acrylic monomersdefined above and the crosslinker monomer(s) as discussed above andwhich is (are) copolymerised with one or more of such acrylic monomersand any crosslinker monomer(s) that is present. Examples of such othermonomers include 1,3-butadiene, isoprene, styrene, α-methyl styrene,divinyl benzene, acrylonitrile, methacrylonitrile, vinyl halides such asvinyl chloride vinyl esters such as vinyl acetate, vinyl propionate,vinyl laurate, and vinyl esters of versatic acid such as VeoVa 9 andVeoVa 10 (VeoVa is a trademark of Shell), heterocyclic vinyl compounds,and alkyl esters of mono-olefinically unsaturated dicarboxylic acid(such as di-n-butyl maleate and di-n-butyl fumarate. Also, in caseswhere they do not provide carboxyl crosslinker groups on polymer Aand/or polymer B (by virtue of there being an absence ofcarboxyl-reactive crosslinker groups also present in or subsequentlyadded to the composition) olefinically unsaturated monocarboxylic ordicarboxylic acids, such as acrylic acid, methacrylic acid,2-carboxyethyl acrylate, fumaric acid, maleic acid, and itacoriic acid.It will be appreciated that such acid monomer(s) may be employed (inpart or in total), once incorporated as polymerised units in the acrylicpolymer, for the provision of pendant amino groups by imination of thecarboxyl groups (as discussed above), particularly in embodiments Y andZ. They could however merely remain in the acrylic polymer as unreactedcarboxyl groups (particularly in embodiment X) because such groupscontribute to improved coating adhesion and also (when present indissociated form) assist in dispersion stability.

Particularly preferred other monomers (i.e. other than acrylic monomersand crosslinker monomers) are selected from acrylic acid and methacrylicacid (in cases where they are not providing crosslinker groups),styrene, acrylonitrile, methacrylamide, and acrylamide.

In embodiment X (the most preferred embodiment as explained above), atypical polymer A or polymer B is derived from a monomer compositionwhich comprises 40 to 98.5 weight % of acrylic monomer(s) (morepreferably 50 to 97 weight %), 0.5 to 20 weight % of crosslinkermonomer(s) (more preferably 1 to 10 weight %) and 1 to 49.5 weight % ofnon-acrylic, non-crosslinker monomer(s) (more preferably 2 to 35 weight%). The acrylic monomer(s) is usefully selected from one or more ofmethyl methacrylate, ethyl acrylate, n-butyl acrylate, n-butylmethacrylate, 2-ethylhexyl acrylate, and 2-ethylhexyl methacrylate; thecrosslinker monomer(s) is usefully selected from one or both ofdiacetone acrylamide and acetoacetoxy ethyl methacrylate and one or moreof acrylic acid, methacrylic acid and 2-carboxyethyl acrylate; and thenon-acrylic, non-crosslinker monomer(s) is usefully selected from one ormore of acrylic acid and methacrylic acid (in cases where such acidmonomer(s) is not providing crosslinker groups), styrene andacrylonitrile.

It will be appreciated that the Tg of an acrylic polymer may be readilycontrolled by appropriate selection of the amounts and types of theconstituent monomers thereof (in terms of the Tg's of the homopolymerswhich would be formed from the constituent monomers if polymerised aloneand their relative amounts). Accordingly polymers A and B could beformed from the same or similar monomer systems, yet be soft or hard byappropriately varying the amounts of the constituent monomers.

The polymerisation of the monomer composition to form an acrylic polymerwill normally require the use of a free-radical-yielding initiator(s) toinitiate the polymerisation. Suitable free-radical-yielding initiatorsinclude inorganic peroxides such as K, Na or ammonium persulphate,hydrogen peroxide, or percarbonates; organic peroxides, such as acylperoxides including for example benzoyl peroxide, alkyl hydroperoxidessuch as t-butyl hydroperoxide and cumene hydroperoxide; dialkylperoxides such as di-t-butyl peroxide; peroxy esters such as t-butylperbenzoate and the like; mixtures may also be used. The peroxycompounds are in some cases advantageously used in combination withsuitable reducing agents (redox systems) such as Na or K pyrosulphite orbisulphite or Na formaldehyde sulphonate, and i-ascorbic acid. Azocompounds such as azoisobutyronitrile may also be used. Metal compoundssuch as Fe.EDTA (EDTA is ethylene diamine tetracetic acid) may also beusefully employed as part of a redox initiator system. An initiatorsystem partitioning between the aqueous and organic phases, for examplea combination of t-butyl hydroperoxide, iso-ascorbic acid and Fe.EDTA,may be of particular use. The amount of initiator or initiator system touse is conventional, for example within the range 0.05 to 6 wt % basedon the total monomer(s) used.

An aqueous polymerisation to form an acrylic polymer normally needs tobe performed in the presence of a stabilising and/or dispersingmaterial, and when making an aqueous latex of an acrylic polymer, aconventional emulsifying agent is employed (e.g. anionic and/or nonionicemulsifiers as such as Na salts of dialkylsulphosuccinates, Na salts ofsulphated oils, Na salts of alkyl sulphonic acids, Na, K and ammoniumalkyl sulphates such as sodium lauryl sulphate, C₂₂₋₂₄ fatty alcohols,ethoxylated fatty acids and/or fatty amides, ethoxylated phenols and Nasalts of fatty acids such as Na stearate and Na oleate; othersurfactants include phosphates, such as the anionic/nonionic surfactantnonylphenol polyglycolether phosphate; the amount used is usually 0.1 to5% by weight on the weight based on the total olefinically unsaturatedmonomer(s) used).

A buffer material, such as sodium bicarbonate, is often employed inpolymerisations to form acrylic polymers.

The polymerisation process may be carried out using an “all-in-one”batch process (i.e. a process in which all the components to be employedare present in the polymerisation medium at the start of polymerisation)or a semi-batch process in which one or more of the components employed(usually at least one of the monomers) is wholly or partially fed to thepolymerisation medium during the polymerisation. Seeded emulsionpolymerisations, oligomer supported polymerisations and miniemulsionpolymerisations may be used.

Molecular weights of polymers may be determined by using gel permeationchromatography using a polymer, e.g. styrene, of known molecular weightas a standard. Where the molecular weight of an acrylic polymer is low,so that the polymer may be considered as an oligomer (e.g. having aweight average molecular weight Mw with the range 5,000 to 100,000g/mole, more preferably 10,000 to 50,000 g/mole), as is particularlyemployed when a sequential polymerisation process is being used to formpolymers A and B where the first formed polymer is often an oligomer (Mwwithin the range defined above) and the second formed polymer is often ahigher Mw polymer (e.g. Mw within the range 100,000 to 3,000,000 g/mole,more preferably 200,000 to 1,000,000 g/mole), the polymerisation to formthe low molecular weight acrylic polymer is preferably performed in thepresence of a chain transfer agent such as one selected from mercaptans(thiols), certain halohydrocarbons and α-methyl styrene, as is quiteconventional. Cobalt chelates may also be employed.

In embodiment X of the invention, wherein an external crosslinking agentis included in, or is subsequently mixed with, the inventioncomposition, and where, as is often preferred, the crosslinkerfunctional groups on one or both of the polymers A and B are carbonylgroups, examples of suitable external crosslinking agents include thefollowing: those compounds having primary and/or secondary amino groups(as these terms are conventionally understood, i.e. bound only to carbonatoms) of 2 to 10 amino groups per molecule, preferably being primaryamines, and specific examples of which include ethylenediamine,propylenediamine, 4-(aminomethyl)-1,8-octanediamine, decamethylenediamine, 1,2-diaminocyclohexane, isophoronediamine,N-2(-hydroxyethyl)ethylenediamine, tris(2-aminoethyl)amine,diethylenetriamine, dipropylenetriamine, dibutylenetriamine,polyethylene imines and the polyalkylene oxide-based di or triaminescommercially available with the “Jeffamine” trade mark (available fromHuntsman Corporation). Also those compounds having 2 or morehydrazine-functional groups, specific examples of which include oxalicacid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide,adipic acid dihydrazide, and sebacic acid dihydrazide, cyclohexanedicarboxylic acid bis-hydrazides, azelaic acid bis-hydrazides; carbonicacid hydrazides, bis-semicarbazides, 1,4-dihyrazinobenzene,2,3-dihydrazinonaphthalene, and dihydrazine. Preferred examples includeadipic acid dihydrazide, carbonic acid dihydrazides, isophorone diamine,Jeffamine T403 (a propoxylated triamine), and 4-(aminomethyl)-1,8-octanediamine.

In embodiment X, the crosslinker functional groups on one or both ofpolymers (A) and (B) may also usefully be carboxyl groups, in which casethe external crosslinking agent is usefully a compound having 2 or moreaziridine groups (a commercially available example being CrosslinkerCX-100™ ex NeoResins, The Netherlands). Also, as discussed above, theexternal crosslinking agent could be a metal compound, such as zincoxide providing zinc cations which can form coordinate bonds by electronpair donation thereto from the oxygen atoms of carboxyl groups. However,such systems are not meant to be limiting and a more comprehensive listof possibilities has been given above.

In embodiment Q (where an external crosslinking agent is also employed)the covalent or coordinate bond-providing crosslinker functional groupson polymer (A) and/or (B) and on the polymer of component (2), areusefully carboxyl groups and the external crosslinking agent is usefullya compound having 2 or more aziridine groups (such as Crosslinker CX100™) or a metal ion providing compound which will allow coordinationbonding. However, such systems are not intended to be limiting and amore comprehensive list of possibilities has been given above.

Typically, the amount of an external crosslinking agent already presentin, or subsequently added to, the invention composition is that toprovide a range of 0.05 to 1.5 moles, more preferably 0.1 to 1.0 moles,of external crosslinker groups present per mole of covalentbond-providing crosslinker groups present on the acrylic polymer(s) ofcomponent (1), and, in the case of embodiment Q, plus the covalentbond-providing crosslinker groups of the polymer of component (2) aswell. In the case of coordinate crosslinking using metal ions andcarboxylic acid groups, the preferred ratio between metal ioncrosslinking functionality and carboxylic acid functionality is 0.05 to1.5 SA more preferred 0.2 to 1.0 SA, defined by metal ion crosslinkingfunctionality to carboxylic acid functionality wherein crosslinkingfunctionality of a zinc ion is defined as 2 and that of a carboxylicacid group as 1.

Turning now more specifically to the self-dispersible, ionicallystabilised and radiation-curable polymer of component (2).

By “ionically-stabilised” is meant that the polymer has ionic internaldispersing groups built into its structure (preferably in pendant and/orterminal positions).

By “self-dispersible” is meant that the polymer forms a stabledispersion in water, as a consequence of its ionic stabilisationresulting from the internal dispersing groups, without the requirementfor added (i.e. external) surfactant(s), although when forming anaqueous dispersion of such a polymer, external surfactant(s) mayoptionally still be employed if desired.

The internal ionic dispersing groups may be of the anionic or cationictype, but are more usually of the anionic type. Usually anionicdispersing groups are provided by carboxyl groups, which need to be intheir neutralised form (carboxylate anionic groups) to effect theirinternal dispersing action. The required amount of dispersing groupscould be achieved by neutralising only a certain proportion of thecarboxyl groups or, alternatively, fully neutralising all such groupsbut having a lower amount of them in the polymer. The use of carboxylgroups providing dispersing groups has the additional benefit that itmay also serve as non-radically-formed covalent bond-providingcrosslinker groups when employing embodiment Q.

Sulphonate ion groups are also useful as anionic dispersing groups.

Nonionic dispersing groups (such as polyoxyethylene groups, PEO) mayalso be present in conjunction with the ionic dispersing groups (theseare also preferably in pendant and/or terminal positions, but may alsobe in-chain).

As discussed above, the groups imparting radiation curability to thepolymer of component (2) are olefinically unsaturated bonds. These arepreferably located in chain-pendant and/or terminal positions, but couldalso possibly be in-chain. The olefinically unsaturated bondfunctionality is preferably at least 0.25 mmoles C=C/g polymer, and ismore preferably in the range of from 0.5 to 3 mmoles C=C/g polymer.

The radiation-curable polymer of component (2) is preferably apolyurethane polymer. Polyurethane polymers are typically prepared fromreactants which comprise an organic polyisocyanate component (usually adiisocyanate component although tri or higher functionality isocyanatescan be employed) and a component comprising a compound(s) bearingNCO-reactive groups, particularly a macro or polymeric polyol (numberaverage molecular weight Mn≧500), optionally with the inclusion of a lowmolecular weight polyol (Mn≦499). Monoisocyanates and monools may alsobe included in the synthesis.

The necessary olefinic unsaturation in the polyurethane (for radiationcurability) could be introduced in a variety of ways. For example, amono or poly (meth)acrylated mono or polyisocyanate could be employed ina urethane synthesis as part of the polyisocyanate component. Moreusually, (meth)acryloyl functional monol or polyol (usually anoligomeric or polymeric monool or polyol, and more usually a diol) couldbe employed as part of the polyol component—such compounds are availablecommercially, and may not need to be synthesised.

The necessary internal ionic dispersing groups for self dispersibilitymay be introduced by employing polyisocyanates or polyols bearing suchgroups in the urethane synthesis (or groups which may be subsequentlyconverted to such groups), preferably the latter. In this regard it isparticularly preferred to employ in the urethane synthesis dihydroxyfunctional alkanoic acid of formula

where R⁴ is H or alkyl (usually 1-5C). More preferably the polyol is2,2-dimethylol propionic acid (DMPA) or 2,2-dimethylol-n-butyric acid(DMBA).

Sulphonate anion dispersing groups for providing self dispersibility(also preferred) may be introduced by employing a sulphonate bearingpolyester polyol in the urethane synthesis; typically an alkali metalsalt of a sulphonic acid substituted aromatic dicarboxylic acid , suchas sodio-5-sulphoisophthalic acid (SSIP), is used in the formation ofthe polyester polyol to provide the sulphonate functionality.

It is, further, preferred that a self-dispersible, ionically stabilisedpolyurethane polymer used as the polymer of component (2) is thechain-extended reaction product of an isocyanate-terminated urethaneprepolymer and an active hydrogen chain-extending compound. Such achain-extended polyurethane preferably has a Mw of at least 3000 g/mole(more preferably Mn of 3,000 to 500,000 g/mole, most preferably 4,000 to250,000 g/mole).

More specifically, it is preferred that a self-dispersible,ionically-stabilised polyurethane polymer employed as the polymer ofcomponent (2) is a chain-extended product formed from reactants whichcomprise:

(A) an aqueous-dispersed isocyanate-terminated prepolymer formed fromreactants which comprise:

(i) at least one organic polyisocyanate;

(ii) at least one isocyanate-reactive component comprising:

(a) at least one polymeric polyol of Mn≧500 and having no internaldispersing groups and no olefinically unsaturated bonds;

(b) at least one polyol bearing ionic internal dispersing groups orgroups which may be converted to such groups;

(c) at least one polyol bearing olefinically unsaturated bonds; and

(B) an active hydrogen chain-extending compound(s).

The organic polyisocyanate(s) A(i) used for making the prepolymer of thepolyurethane is preferably an organic diisocyanate(s). Such organicpolyisocyanate(s) may be an aliphatic (which term includescycloaliphatic), araliphatic or aromatic polyisocyanate. Preferably,however, the polyisocyanate(s) is aliphatic.

Examples of suitable aliphatic polyisocyanates include ethylenediisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate,cyclohexane-1,4-diisocyanate, 4,4′-dicyclohexylmethane diisocyanate,cyclopentylene diisocyanate, p-tetramethyl xylylene diisocyanate(p-TMXDI) and its meta isomer (m-TMXDI), hydrogenated 2,4-toluenediisocyanate, hydrogenated 2,6-toluene diisocyanate, and1-isocyanato-1-methyl-3(4)-isocyanatomethyl-cyclohexane (IMCI).Polyisocyanate trimers, e.g. trimers of hexamethylene diisocyanate(isocyanurate, biuret type) can also be employed.

Suitable non-aliphatic polyisocyanates include p-xylylene diisocyanate,1-4-phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluenediisocyanate, 4,4′-diphenylmethane diisocyanate, 2,4-diphenylmethanediisocyanate, and 1,5-naphthylene diisocyanate.

Mixtures of polyisocyanates can be used and also polyisocyanates whichhave been modified by the introduction or urethane, allophanate, urea,biuret, carbodiimide, uretonimine, uretidione or isocyanurate residues.

Preferred polyisocyanates are cycloaliphatic polyisocyanates such as4,4′-dicyclohexylmethane diisocyanate and isophorone diisocyanate.

The polymeric polyol(s) A (ii)(a) of the isocyanate-reactive componentA(ii) is preferably a polymeric diol, but may be or include polymericpolyol(s) of functionality more than 2. The polymeric polyol(s)preferably has a number average molecular weight (hereinafter Mn) withinthe range of from 500 to 8,000 g/mole, more preferably from 700 to 7,000g/mole. Such polyol(s) is preferably essentially linear. Such polyol(s)in principle may be selected from any of the chemical classes ofpolymeric polyols used or proposed to be used in polyurethane synthesis.More preferably the polymeric polyol(s) is selected from a polyesterpolyol and a polyether polyol, and particularly preferably is apolyester polyol.

Polyols having Mn below 500 (which may be polymeric, or ratheroligomeric, or monomeric) and having no internal dispersing groups andolefinically unsaturated bonds may optionally be used as part of theisocyanate-reactive component A(ii) in the preparation of theisocyanate-terminated prepolymer. Examples particularly include diolsand (less preferably) triols or tetrols and mixtures thereof. Examplesof such lower molecular weight polyols include ethylene glycol,1,4-cyclohexane dimethanol and furan dimethanol, trimethylolpropane andglycerol.

It will be appreciated that the isocyanate-reactive component A(ii) mayoptionally include an isocyanate-reactive compound(s) which is otherthan a polyol (e.g. a diamine or an aminoalcohol); however the polyolcomponent will normally be entirely or substantially comprised of polyolreactant(s).

The ionic dispersing groups of A(ii)(b) may be cationic, or morepreferably, anionic, for example —SO₃ ⁻, —OSO₃ ⁻, —CO₂ ⁻, —PO₃ ⁻, and—OPO₃ ³ ³¹ and in particular carboxylate anion groups —CO₂ ⁻ andsulphonate anion groups —SO₃ ⁻.

Groups which are subsequently converted to dispersing groups areparticularly unionised (or substantially unionised) acid or basic groupswhich can be e.g. converted to corresponding anionic or cationic groupsby neutralisation or quaternisation. For example free (unionised)carboxylic acid groups can be neutralised to carboxylate anionic groupswhile tertiary amine groups can be quaternised to quaternary ammoniumgroups.

It is most preferred that ionic groups are incorporated into theprepolymer via anionic group-containing polyols or potentially anionicgroup-containing polyols which can be subsequently neutralised to formanionic groups using agents such as a tertiary amine, examples of whichinclude triethylamine, triethanolamine or N-methylmorpholine, or analkaline hydroxide such as K, Na or Li hydroxide or a quaternaryammonium hydroxide. Ammonia itself may also be used.

It is most preferred (as indicated above) that the reactants forintroducing carboxylate anionic dispersing groups are dihydroxyalkanoicacids of formula 2, especially DMPA and DMBA.

The conversion of any acid groups present in the prepolymer to anionicsalt groups may be effected by neutralising the acid groups before,after, or simultaneously with the formation of an aqueous dispersion ofthe prepolymer.

The component A(ii) may optionally include polyols bearing nonionicdispersing groups, typically polyethylene oxide groups (PEO groups) forintroducing nonionic dispersing groups into the polyurethane.

Generally speaking, it is preferred to use within the range of from 0.1to 1.1 (more preferably 0.2 to 0.75 and most preferably 0.25 to 0.6)milliequivalents of ionic (preferably anionic) internal dispersinggroups per g of solid polyurethane prepolymer. In the case of optionalnonionic internal dispersing groups (such as PEO chains), it is,generally speaking, preferred to use 0 to 25 weight % (more preferably 4to 12 weight %) of such groups per g of solid polyurethane polymer.Optionally external nonionic surfactants (e.g. 0-5 weight %) could beemployed to facilitate dispersing and stability.

The at least one polyol bearing olefinically unsaturated bonds ispreferably a polyol bearing acryloyl or methacryloyl groups (asmentioned above). Preferably an unsaturated double bond functionalityshould be provided in the resulting polyurethane as a whole of at least0.25 mmoles C=C/g polyurethane, more preferably 0.5 to 3 mmoles/gpolyurethane.

The isocyanate-terminated polyurethane prepolymer may be prepared inconventional manner by reacting a stoichiometric excess of the organicpolyisocyanate(s) with the isocyanate-reactive component (and any otherreactants) under substantially anhydrous conditions at a temperaturebetween about 30° C. and about 130° C. until reaction between theisocyanate groups and the isocyanate-reactive (usually all hydroxyl)groups is substantially complete. During the production of theisocyanate-terminated prepolymer the reactants are generally used inproportions corresponding to a ratio of isocyanate groups toisocyanate-reactive (usually all hydroxyl) groups from about 1.1:1 toabout 6:1, preferably from about 1.5:1 to 3:1 (particularly 1.5:1 to2:1). It is preferred to carry out the reaction to form the prepolymerin the presence of a small amount of a radical scavenger, such as2,6-di-tert-butyl-4-methylphenol, to avoid any adverse effect on theolefinically unsaturated bonds (particularly when an elevatedtemperature is being used).

If desired, catalysts such as dibutyltin dilaurate or stannous octoatemay be used to assist prepolymer formation. An organic solvent mayoptionally be added before, during or after prepolymer formation tocontrol the viscosity preferably provided it does not vitiate theobtaining of a solvent-free final dispersion (such solvent may thussubsequently need to be removed as far as is possible). Suitablesolvents which may be used are preferably water-miscible solvents suchas N-methylpyrrolidone and methyl ethyl ketone.

The aqueous polyurethane dispersion can be formed according to a varietyprocesses known to those skilled in the art. The aqueous polyurethanedispersion when formed using a prepolymer/chain extension synthesis isprepared by forming an aqueous dispersion of the isocyanate-terminatedpolyurethane prepolymer and dispersing it (optionally carried in anorganic solvent medium) in an aqueous medium, utilisingself-dispersibility properties of the prepolymer arising from internaldispersing groups in the isocyanate-terminated prepolymer, although freesurfactant(s) may additionally be employed if desired, and chainextending the prepolymer with an active hydrogen compound(s) in theaqueous phase, the chain extender being present in the aqueous phaseduring dispersion or added subsequently (i.e. chain-extension can takeplace during and/or after the dispersion into water).

In another option (although less preferred) small amounts of reactivediluent can be used instead of solvents to reduce prepolymer viscosityduring synthesis. Typically 2-6 weight % on total system and not morethan 10 weight %, more preferred not more than 7 weight % on totalsystem.

The prepolymer may be dispersed in water using techniques well known inthe art. Preferably, the prepolymer is added to the water with agitationor, alternatively, water may be stirred into the prepolymer component.

The active hydrogen-containing chain extender compound(s) which may bereacted with the prepolymer component is suitably a primary or secondaryaliphatic, alicyclic, aromatic, araliphatic or heterocyclic diamine orpolyamine (i.e. having 3 or more amine groups as this term isconventionally understood, i.e. linked to C only), or hydrazine or asubstituted hydrazine, or a polyhydrazide (preferably a dihydrazide).

Water-soluble chain extenders are preferred.

Water itself may be used as an indirect chain extender because it willslowly convert some of the terminal isocyanate groups of the prepolymerto amino groups (via unstable carbamic acid groups) and the modifiedprepolymer molecules will then undergo chain extension. However, this isvery slow compared to chain extension using the above mentioned activehydrogen chain extenders (which can be called added chain extendercompounds) which will provide the predominant chain extension reactionif used.

Examples of such added chain extenders useful herein include ethylenediamine, diethylene triamine, triethylene tetramine, propylene diamine,butylene diamine, hexamethylene diamine, cyclohexylene diamine,piperazine, 2-methyl piperazine, phenylene diamine, toluene diamine,xylylene diamine, tri (2-aminoethyl) amine, 3,3-dinitrobenzidine,4,4′-diaminodiphenylmethane, methane diamine, isophorone diamine, andadducts of diethylene triamine with acrylate or its hydrolysed products.Also materials such as hydrazine (e.g. in the form of its mono hydrate),azines such as acetone azine, substituted hydrazines such as, forexample, dimethyl hydrazine, 1,6-hexamethylene-bis-hydrazine,carbodihydrazine, dihydrazides of dicarboxylic acids and sulphonic acidssuch as adipic acid dihydrazide, oxalic acid dihydrazide, isophthalicacid dihydrazide, hydrazides made by reacting lactones with hydrazinesuch as gamma-hydroxylbutyric hydrazide, bis-semi-carbazide, andbis-hydrazide carbonic esters of glycols.

Preferably the active hydrogen chain extender component is or includeshydrazine (usually in the form of its monohydrate), or a di or triamine(usually a diamine such as ethylene diamine or isophorone diamine) of Mnbelow 300.

When the chain extender is an added component, i.e. is other thanmodified prepolymer molecules formed by reaction with water, for examplea polyamine or diamine or hydrazine, it may e.g. be added to the aqueousdispersion of prepolymer, or it may e.g. already be present in theaqueous medium when the prepolymer is dispersed therein, or it may e.g.simply be fed with prepolymer to water.

The chain extension can be conducted at elevated, reduced or ambienttemperatures. Convenient temperatures are from about 5° C. to 90° C.,more preferably 10° C. to 60° C.

The total amount of chain extender material(s) employed (other thanwater) is preferably such that the ratio of active hydrogens in thechain extender(s) to NCO groups in the prepolymer component ispreferably within the range of from 0.7/1 to 2.0/1 more preferably0.85/1 to 1.2/1. Of course, when water is employed as an indirect chainextender, these ratios will not be applicable since the water,functioning both as an indirect chain extender and a dispersing medium,will be present in a gross excess relative to the residual NCO groups.

It is evident from all the foregoing that the term “polyurethane” asused in this specification is intended to apply not only to polymers (orprepolymers) having only urethane linkages formed from isocyanate andhydroxyl groups, but also to polymers, prepolymers or polymer segmentshaving, in addition to urethane linkages, linkages formed fromisocyanate groups and groups such as —NH₂, —NH—, or —SH groups.

The components (1) and (2) of the invention composition may be combinedby any suitable method, although a simple blending procedure isfavoured. Another possibility would be to form the radiation-curablepolymer of component (2) in the presence of the acrylic polymers ofcomponent (1).

The weight ratio of the polymers of component (1) to the polymer ofcomponent (2) is preferably within the range of from 20/80 to 97/3, morepreferably 45/55 to 90/10.

By Tg herein is meant the glass transition temperature, the Tg of apolymer, as is well known, being the temperature at which it changesfrom a rubbery or plastic state to a glassy or brittle state. It may bedetermined experimentally e.g. by differential scanning calorimetry, orcalculated from the well known Fox equation, wherein the Tg, in degreesKelvin, of a copolymer having “n” copolymerised comonomers is given bythe weight fractions W of each comonomer type and the Tg's of thehomopolymers (in degrees Kelvin) derived from each comonomer accordingto the equation:$\frac{1}{Tg} = {\frac{W_{1}}{{Tg}_{1}} + \frac{W_{2}}{{Tg}_{2}} + {\ldots \quad \frac{W_{n}}{{Tg}_{n}}}}$

The minimum film forming temperature (MFT) of an aqueous composition asused herein is the temperature where the composition forms a smooth andcrackfree coating or film using DIN 53787 and applied using a Sheen MFFTbar SS3000.

Koenig hardness as used herein is a standard measure of hardness, beinga determination of how the viscoelastic properties of a film formed fromthe dispersion slows down a swinging motion deforming the surface of thefilm, and is measured according to DIN 53157 NEN 5319 using an Erichsenhardness equipment.

The solids content of an aqueous composition of the invention is usuallywithin the range of from about 20 to 65 wt % on a total weight basis,more usually 32 to 55 wt %. Solids content can, if desired, be adjustedby adding water or removing water (e.g. by distillation orultrafiltration).

The aqueous composition of the invention may be used in variousapplications and for such purposes may be further optionally combined orformulated with other additives or components such as defoamers,rheology control agents, thickeners, dispersing and stabilising agents(usually surfactants), wetting agents, fillers, extenders, fungicides,bacteriocides, anti-freeze agents, waxes and pigments.

The aqueous dispersions may e.g. be used, appropriately formulated ifnecessary, for the provision of films, polishes, varnishes, lacquers,paints, inks and adhesives. However, they are particularly useful andsuitable for providing the basis of protective coatings for woodensubstrates (e.g. wooden floors), and plastics, paper, leather and metalsubstrates.

The dispersions (or compositions) once applied may be allowed to drynaturally at ambient temperature, or the drying process may beaccelerated by heat (e.g. using an infrared source).

The present invention is now further illustrated but in no way limitedby reference to the following examples. Unless otherwise specified allparts, percentages, and ratios are on a weight basis. The prefix Cbefore an example number denotes that it is comparative. All Tg's werecalculated using the Fox equation (unless specified otherwise).

Preparation of a Crosslinkable Aqueous Emulsion of an Acrylic PolymerCombination Containing External Crosslinking Agent (AP1)

A combination of hard and soft carbonyl functional acrylic polymers wasprepared using a sequential polymerisation process as follows.

To a round-bottomed flask equipped with a condenser, thermometer andmechanical stirrer 910.8 parts of water, 1 part of sodium bicarbonate,and 3.1 parts of Surfagene FAZ109V (nonylphenol polyglycoletherphosphate) were charged. This mixture was heated to 85° C. At 75° C., 5%of a monomer feed consisting of 216.9 parts of water, 362.8 parts ofmethyl methacrylate, 39.6 parts of diacetone acrylamide, 31.7 parts ofmethacrylic acid, 59.8 parts of ethyl acrylate, 9.3 parts of SurfageneFAZ109V, 0.5 parts of sodium bicarbonate, and 22.3 parts of laurylmercaptane was added. At 80° C., 30% of an initiator feed consisting of1.5 parts of ammonium persulphate and 97.5 parts of water was added. 5minutes after the temperature reached 85° C. a start was made with theaddition of the remainders of the monomer and initiator feeds. Themonomer feed was added over a period of 60 minutes, while the initiatorfeed was added over a period of 70 minutes. At the end of the additionof the initiator feed 39.2 parts of water were used to rinse the feedtank and were added to the reactor. A temperature of 85° C. wasmaintained for 30 minutes after which the reaction mixture was cooled to80° C. At 80° C. the resulting polymer emulsion was neutralised using56.6 parts of a 25% solution of ammonia in water. The reaction mixturewas subsequently kept at 80° C. for another 30 minutes before it wascooled to ambient temperature.

The resulting acrylic polymer emulsion had a solids content of 27.2% anda pH of 10.2. The Tg of this first formed acrylic polymer was 85° C.

To a round-bottomed flask equipped with a condenser, thermometer andmechanical stirrer 94.3 parts of water, 0.8 parts of ammoniumpersulphate and 183.1 parts of the aqueous emulsion of the hard acrylicpolymer formed as above were added. 10% of a monomer feed consisting of219.8 parts of water, 277.0 parts of n-butyl methacrylate, 85.4 parts ofn-butyl acrylate, 11.2 parts of diacetone acrylamide, 274.7 parts of theaqueous emulsion of the hard acrylic polymer formed as above and 0.4parts of dimethyl ethanol amine was added after which the temperaturewas raised to 85° C. At 85° C. the remainder of the monomer feed wasadded to the reactor over a period of 90 minutes. At the same time themonomer feed was started, an initiator feed consisting of 43.7 parts ofwater and 1.1 part of ammonium persulphate was started, which shouldtake 100 minutes. After addition of the monomer feed to the reactor thefeed tank was rinsed with 147.3 parts of water, which were subsequentlyadded to the reactor. After the initiator feed was added, thetemperature was kept at 85° C. for 30 minutes after which the reactionmixture was cooled to room temperature.

The Tg of the soft, second-formed acrylic polymer (formed in thepresence of the first-formed hard acrylic) was 3° C.

To the resulting polymer aqueous emulsion was added a mixture of 10.7parts of the external crosslinking agent adipic acid dihydrazide (ADH)and 20 parts of water. The final aqueous emulsion had a solids contentof 37.4% and a pH of 9.2. The system is crosslinkable on coating formingaccording to embodiment X by reaction of the carbonyl groups with thehydrazide groups of the external crosslinking agent ADH.

Preparation of a Crosslinkable Aqueous Emulsion of an Acrylic PolymerCombination Containing External Crosslinking Agent (AP2)

A combination of hard and soft carbonyl functional acrylic polymers wasprepared using a sequential polymerisation process as follows.

To a round-bottomed flask equipped with a condenser, thermometer andmechanical stirrer 0.8 parts of ammonium persulphate and 533.3 parts ofthe aqueous emulsion of the hard acrylic polymer formed as above in AP1were added. 10% of a monomer feed consisting of 213.4 parts of water,268.9 parts of n-butyl methacrylate, 82.9 parts of n-butyl acrylate,10.9 parts of diacetone acrylamide, 800.0 parts of the hard acrylicpolymer emulsion and 0.4 parts of dimethyl ethanol amine was added afterwhich the temperature was raised to 85° C. At 85° C. the remainder ofthe monomer feed was added to the reactor over a period of 90 minutes.At the same time as the monomer feed was started, an initiator feedconsisting of 42.4 parts of water and 1.1 part of ammonium persulphatewas started, which should take 100 minutes. After the initiator feed wasadded the temperature was kept at 85° C. for 30 minutes after which thereaction mixture was cooled to ambient temperature. The Tg of the soft,second-formed acrylic polymer (formed in the presence of thefirst-formed hard acrylic polymer formed as above in AP1 was 3° C.

To resulting aqueous polymer emulsion was added a mixture of 19.8 partsof the external crosslinking agent adipic acid dihydrazide and 11.6parts of water. The final aqueous emulsion had a solids content of 37.4%and a pH of 9.8. The system is crosslinkable according to embodiment Xon coating formation by reaction of the carbonyl groups with thehydrazide groups of the external crosslinking agent ADH.

Preparation of an aqueous dispersion of a Radiation Curable Polymer (R1)

A self-dispersible uv-curable polyurethane polymer in accordance withcomponent (2) of the invention composition was prepared as follows.

To a round-bottomed flask equipped with a thermometer and mechanicalstirrer, 330.7 parts of isophorone diisocyanate, 37.5 parts ofdimethylol propionic acid, 52.5 parts of an acryloyl functional polyolCN104 (OH number=233.9 mg KOH/g; Cray Valley, France), 329.3 parts of apolyester diol S-1063-120 (OH number=120 mg KOH/g; Occidental Chemical,Belgium), 0.15 parts of 2,6-di-tert-butyl-4-methylphenol (lonol CP) and0.15 parts of tin octoate were added and slowly heated to 95° C. under adry air atmosphere. The mixture was held at this temperature until theNCO content was 8.04%. Subsequently 28.3 parts of triethylamine wereadded to the reaction mixture. 500 parts of this mixture were dispersedinto 905 parts water during 1 hour to form an aqueous dispersion of theNCO-terminated prepolymer. Thereafter 22.9 parts of hydrazine were addedas a 64.5% solution in water to chain-extend the prepolymer. Theresulting translucent polyurethane dispersion had a solids content of34.6% and a pH of 8.0. The unsaturated bond functionality was 0.57mmoles C=C/g polymer.

Preparation of an Aqueous Emulsion of a Radiation-Curable Oligomer (R2)

A uv-curable urethane oligomer not in accordance with component (2) ofthe invention composition (by virtue of not being self-dispersible) andfor use in comparative examples(see following Examples C2 and C5), wasprepared as follows.

To a round-bottomed flask equipped with a thermometer, dropping funneland mechanical stirrer 461.3 parts of tetra-methyl-m-xylylenediisocyanate, 0.45 parts of 2,6-di-tert.-butyl-4-methylphenol (lonol CP)and 0.2 parts of tin octoate were added and slowly heated to 90° C.438.6 parts of hydroxyethyl acrylate were added dropwise to this mixtureduring 60 minutes. This mixture was held at 95° C. until the NCO contentwas below 0.2%. The resulting acryloyl functional urethane oligomer wasa slightly yellow viscous liquid. Because this urethane is notself-dispersing it was emulsified according to the following recipe.

Composition Supplier RO1 Viscous liquid urethane — 75.0 Triton X100Union Carbide 2.5 Water — 22.5

NB This emulsion was prepared at 80° C., adding to a vessel the viscousliquid urethane and Triton X100 (alkylphenol ethoxylate), and then withvigorous mixing using a Dispersmat stirrer, slowly adding water during15 minutes to give a stable and creamy emulsion.

Preparation of an Aqueous Emulsion of a Radiation Curable Monomer (R3)

The intention here was to prepare an aqueous emulsion of a uv-curablemonomer, trimethylol propane tri-acrylate (TMPTA) (i.e. not inaccordance with component (2)) for use in comparative examples (seefollowing Examples C3 and C6).

TMPTA is not self-dispersible and so was emulsified in water using thefollowing ingredients.

emulsified TMPTA Compound Supplier (parts) TMPTA BASF 75.0 Triton X100Union Carbide 2.5 Water — 22.5

The emulsion was prepared at room temperature, adding to a vessel theTMPTA and Triton X100, and then vigorously mixing using a Dispermatstirrer, slowly adding water during 20 minutes to give a creamy andstable emulsion.

EXAMPLES 1, C2, C3, 4, C5 AND C6

Aqueous polymer compositions were prepared by mixing the acrylic polymeremulsions AP1 and AP2 with the emulsions of the uv-curable R1, R2, andR3, as shown in the following Table 1. Examples 1 and 4 are according tothe invention (the acrylic polymer system crosslinkability being byembodiment X), while Examples C2, C3, C5 and C6 are comparative examplesfor the reasons explained above. In each composition the ratio of theacrylic polymer component (i.e. including both acrylic polymers) to theuv-curable compound was 70/30 (solids:solids).

3 parts of the photoinitiator Darocure 1173 (Ciba Geigy) were added per100 parts of each dispersion and films were subsequently cast with awire rod on test charts to a wet-film thickness of 125 micrometers andalso cast with a film applicator to a thickness of 80 micrometers onglass plates. Drying was carried out rapidly at 60° C. and the coatedtest charts and glass plates were passed twice under a high pressuremercury lamp (120 watts/cm, wave length 240 nm) at 10 m/minutes. Thiseffected uv-curing, with covalent crosslinking also having taken placeat ambient temperature after drying by reaction of the carbonyl groupson the acrylic polymers and the hydrazide groups on the ADH crosslinkingagent.

The dispersion stability of a sample of each composition was monitoredat 52° C. as an accelerated stability test and any gel formation orphase separation of the dispersion was assessed as corresponding to anunstable dispersion. (The figures>1 week for Example 1 and 4 indicatethat the dispersion was still stable after 1 week); the term “unstable”for Examples C2, C3, C5 and C6 means that the dispersions rapidly becameunstable at 52° C.).

The hardness of the cured films was measured on the glass plates using aPendulum Hardness Tester according to the Koenig test method.

Xylene rub tests (being a measure of the resistance of the coating toxylene solvent) were performed on the coated glass plates using cottonwool soaked with xylene which was rubbed over the surface of thecoating, the number of rubs before failure being listed.

Resistance to blocking was carried out using “early blocking” and“normal blocking” tests with a block tester both before uv applicationand after uv application with films coated on paper test charts andrapidly dried at 60° C. In the normal blocking test the films were agedfor 16 hours at 52° C. in an oven. Next, pairs of the coated test chartswere placed with the film coatings face to face and left at 52° C. for 4hours with a pressure of 1 kg/cm². In the early blocking test, the filmswere aged at 60° C. for 20 minutes after which the face to face pairs ofcoated test charts were pressed for 4 hours with a pressure of 3 kg/cm².After cooling to ambient temperature in each test, the test charts werepeeled and the degree of block resistance assessed, ranging from 0 (verypoor blocking resistance) to 5 (excellent blocking resistance).

The results of the above testing are shown in the following Table 1. Itis apparent that the use of non-self-dispersible radiation curablecomponents in the compositions not only resulted in inferior dispersionstability but also (for the most part) in inferior hardness, xyleneresistance and blocking resistance.

TABLE 1 Acrylic uv-curable Early Blocking Normal Blocking Componentcompound Embodiment 52° C. Hardness Before uv After uv Before uv Afteruv Ex. No emulsion dispersion of Invention stability (sec) Xylene rubscure cure cure cure 1 AP1 R1 X >1 week 64 38 2 3 4 4-5 C2 AP1 R2 —unstable 52 28 0 0 0 0 C3 AP1 R3 — unstable tacky 20 0 0 0 0 4 AP2 R1X >1 week 108  67 0 0-1 4-5 4 C5 AP2 R2 — unstable 162  >100  0 0 0 0 C6AP2 R3 — unstable 78 52 0 0 0 0

Preparation of a Non-crosslinkable Aqueous Emulsion of an AcrylicPolymer Combination Containing no External Crosslinking Agent (AP3)

A combination of hard and soft acrylic polymers, the hard acrylicpolymer being carboxyl functional, was prepared using a sequentialpolymerisation process as follows.

To a round-bottomed flask equipped with a condenser, thermometer andmechanical stirrer 910.8 parts of water, 1 part of sodium bicarbonate,and 3.1 parts of Surfagene FAZ109V were charged. This mixture was heatedto 85° C. At 75° C., 5% of a monomer feed consisting of 216.9 parts ofwater, 393.4 parts of methyl methacrylate, 32.7 parts of methacrylicacid, 68.8 parts of ethyl acrylate, 9.3 parts of Surfagene FAZ109V, 0.5parts of sodium bicarbonate, and 22.3 parts of lauryl mercaptane wasadded. At 80° C., 30% of a catalyst feed consisting of 1.5 parts ofammonium persulphate and 97.5 parts of water was added. 5 minutes afterthe temperature reached 85° C. a start was made with the addition of theremainders of the monomer and catalyst feeds. The monomer feed was addedover a period of 60 minutes, while the catalyst feed was added over aperiod of 70 minutes. At the end of the addition of the catalyst feed39.2 parts of water were used to rinse the feed tank and were added tothe reactor. A temperature of 85° C. was maintained for 30 minutes afterwhich the reaction mixture was cooled to 80° C. At 80° C. the emulsionwas neutralised using a mixture of 56.6 parts of a 25% solution ofammonia in water and 56.6 parts of water. The reaction mixture wassubsequently kept at 80° C. for another 30 minutes before it was cooledto room temperature.

The resulting acrylic polymer emulsion had a solids content of 27.2% anda pH of 10.2. The Tg of this first formed hard acrylic polymer was 85°C.

To a round-bottomed flask equipped with a condenser, thermometer andmechanical stirrer, 0.8 parts of ammonium persulphate, and 549.4 partsof the aqueous emulsion of the hard acrylic polymer formed as above wereadded. 10% of a monomer feed consisting of 209.8 parts of water, 293.3parts of n-butyl methacrylate, 80.3 parts of n-butyl acrylate, 824.1parts of the aqueous emulsion of the hard acrylic polymer formed asabove and 0.4 parts of dimethyl ethanol amine was added after which thetemperature was raised to 85° C. At 85° C., the remainder of the monomerfeed was added to the reactor over a period of 90 minutes. At the sametime as the monomer feed was started, a catalyst feed consisting of 43.7parts of water and 1.1 part of ammonium persulphate was started, whichshould take 100 minutes. After the catalyst feed had been added thetemperature was kept at 85° C. for 30 minutes after which the reactionmixture was cooled to room temperature. The Tg of the soft, secondformed acrylic polymer (formed in the presence of the first-formed hardacrylic) was 0° C.

The resulting acrylic polymer emulsion had a solids content of 37.4% anda pH of 9.2. The system is not crosslinkable on coating formationaccording to embodiment X by virtue of not containing an externalcrosslinking agent having groups which can react with the carboxylgroups in the acrylic polymer combination (the only potentialcrosslinker groups therein).

Preparation of a Crosslinkable Aqueous Emulsion of an Acrylic PolymerCombination Containing an External Crosslinking Agent (AP4)

A combination of hard and soft carbonyl functional acrylic polymers wasprepared using a sequential polymerisation process as follows.

To a round-bottomed flask equipped with a condenser, thermometer andmechanical stirrer 910.8 parts of water, 1 part of sodium bicarbonate,and 3.1 parts of Surfagene FAZ109V were charged. This mixture was heatedto 85° C. At 75° C., 5% of a monomer feed consisting of 216.9 parts ofwater, 362.8 parts of methyl methacrylate, 39.6 parts of diacetoneacrylamide, 32.7 parts of methacrylic acid, 59.8 parts of ethylacrylate, 9.3 parts of Surfagene FAZ109V, 0.5 parts of sodiumbicarbonate, and 22.3 parts of lauryl mercaptane was added. At 80° C.,30% of a catalyst feed consisting of 1.5 parts of ammonium persulphateand 97.5 parts of water was added. 5 minutes after the temperature hadreached 85° C., a start was made with the addition of the remainders ofthe monomer and catalyst feeds. The monomer feed was added over a periodof 60 minutes, while the catalyst feed was added over a period of 70minutes. At the end of the addition of the catalyst feed 39.2 parts ofwater were used to rinse the feed tank and were added to the reactor. Atemperature of 85° C. was maintained for 30 minutes after which thereaction mixture was cooled to 80° C. At 80° C. the emulsion wasneutralised using a mixture of 56.6 parts of a 25% solution of ammoniain water and 56.6 parts of water. The reaction mixture was subsequentlykept at 80° C. for another 30 minutes before it was cooled to roomtemperature. The resulting acrylic polymer emulsion had a solids contentof 27.2%. The Tg of this first formed hard acrylic polymer was 85° C.

To a round-bottomed flask equipped with a condenser, thermometer andmechanical stirrer, 0.7 parts of ammonium persulphate, and 533.3 partsof the aqueous emulsion of the hard acrylic polymer formed as above wereadded. 10% of a monomer feed consisting of 213.4 parts of water, 351.8parts of n-butyl methacrylate, 10.9 parts of diacetone acrylamide, 800.0parts of the aqueous emulsion of the hard acrylic polymer formed asabove and 0.4 parts of dimethyl ethanol amine was added after which thetemperature was raised to 85° C. At 85° C., the remainder of the monomerfeed was added to the reactor over a period of 90 minutes. At the sametime as the monomer feed was started, a catalyst feed consisting of 42.4parts of water and 1.1 part of ammonium persulphate was started, whichshould take 100 minutes. After the catalyst feed had been added thetemperature was kept at 85° C. for 30 minutes after which the reactionmixture was cooled to room temperature.

At room temperature a solution of 19.8 parts of adipic dihydrazide and11.6 parts of water was added. The Tg of the soft, second formed acrylicpolymer (formed in the presence of the first formed hard acrylicpolymer) was 21° C. The final aqueous emulsion had a solids content of37.8%. The system is crosslinkable on coating formation according toembodiment X by reaction of the carbonyl groups with the hydrazidegroups of the external crosslinking agent ADH.

Preparation of a Crosslinkable Aqueous Emulsion of an Acrylic PolymerCombination Containing an External Crosslinking Agent (AP5)

A combination of hard and soft carbonyl functional polymers was preparedusing a sequential polymerisation process as follows.

To a round-bottomed flask equipped with a condenser, thermometer andmechanical stirrer, 993.3 parts of water and 8.3 parts of SurfageneFAZ109V were charged. This mixture was heated to 85° C. At 50° C., 10%of a monomer feed consisting of 110.9 parts of water, 270.5 parts ofmethyl methacrylate, 29.5 parts of diacetone acrylamide, 24.4 parts ofmethacrylic acid, 44.6 parts of ethyl acrylate and 24.9 parts ofSurfagene FAZ109V was added. At 75° C., 30% of a catalyst feedconsisting of 1.6 parts of ammonium persulphate and 30.1 parts of waterwas added. As soon as the reaction temperature had been reached theremainders of the monomer feed and catalyst feed were added over aperiod of 60 minutes. At the end of the monomer feed the feed tank wasrinsed with 10.9 parts of water, which was subsequently added to thereactor. The polymerisation mixture was kept at 85° C. for 60 minutesbefore starting the second monomer and catalyst feeds. These consistedof 1.2 parts of water, 273.6 parts of n-butyl methacrylate, 84.4 partsof n-butyl acrylate and 11.1 parts of diacetone acrylamide for themonomer feed and 1.6 parts of ammonium persulphate and 30.1 parts ofwater for the catalyst feed, respectively. Next the mixture was kept atpolymerisation temperature for 30 minutes. Free monomer was furtherreduced by adding a mixture of 0.7 parts of iso-ascorbic acid and 14.0parts of water followed by a mixture of 0.9 parts of an 80 weight-%solution of t-butyl hydroperoxide in water and 1.5 parts of water.Temperature was maintained at 85° C. for another 30 minutes before 15.4parts of a 12.5 weight-% solution of ammonia in water and 20.6 parts ofadipic dihydrazide were added. The resulting emulsion had a solidscontent of 37.5%. The Tg of the first formed hard acrylic polymer was85° C., and that of the second formed soft acrylic polymer was 0° C. Thesystem is crosslinkable according to embodiment X on coating formationby reaction of the carbonyl groups with the hydrazide groups of theexternal crosslinking agent ADH.

Preparation of a Crosslinkable Aqueous Emulsion of an Acrylic PolymerCombination Containing no External Crosslinking Agent (AP6)

A combination of a hard acrylic polymer bearing amino groups and a softacrylic polymer bearing carbonyl groups was prepared using a sequentialpolymerisation process as follows.

To a round-bottomed flask equipped with a condenser, thermometer andmechanical stirrer, 910.8 parts of water, 1 part of sodium bicarbonate,and 3.1 parts of Surfagene FAZ109V were charged. This mixture was heatedto 85° C. At 75° C., 5% of a monomer feed consisting of 216.9 parts ofwater, 393.4 parts of methyl methacrylate, 32.7 parts of methacrylicacid, 68.8 parts of ethyl acrylate, 9.3 parts of Surfagene FAZ109V, 0.5parts of sodium bicarbonate, and 22.3 parts of lauryl mercaptane wasadded. At 80° C., 30% of a catalyst feed consisting of 1.5 parts ofammonium persulphate and 97.5 parts of water was added. 5 minutes afterthe temperature had reached 85° C., a start was made with the additionof the remainders of the monomer and catalyst feeds. The monomer feedwas added over a period of 60 minutes, while the catalyst feed was addedover a period of 70 minutes. At the end of the addition of the catalystfeed, 39.2 parts of water were used to rinse the feed tank and wereadded to the reactor. A temperature of 85° C. was maintained for 30minutes after which the reaction mixture was cooled to 80° C. At 80° C.the emulsion was neutralised using a mixture of 56.6 parts of a 25%solution of ammonia in water and 56.6 parts of water. The reactionmixture was subsequently kept at 80° C. for another 30 minutes before itwas cooled to room temperature. The resulting acrylic polymer emulsionhad a solids content of 27.2% and a pH of 10.2. The Tg of this firstformed hard acrylic polymer was 85° C.

To a round-bottomed flask equipped with a condenser, thermometer andmechanical stirrer, 0.7 parts of ammonium persulphate, and 533.3 partsof the aqueous emulsion of the hard acrylic polymer formed as above wereadded. 10% of a monomer feed consisting of 213.4 parts of water, 274.1parts of n-butyl methacrylate, 77.7 parts of n-butyl acrylate, 10.9parts of acetoacetoxy ethylmethacrylate, 824.1 parts of the aqueousemulsion of the hard acrylic polymer formed as above and 0.4 parts ofdimethyl ethanol amine was added, after which the temperature was raisedto 85° C. At 85° C., the remainder of the monomer feed was added to thereactor over a period of 90 minutes. At the same time as the monomerfeed was started, a catalyst feed consisting of 43.7 parts of water and1.1 part of ammonium persulphate was started, which should take 100minutes. After the catalyst feed was added the temperature was kept at85° C. for 30 minutes after which the reaction mixture was cooled to 55°C. At 55° C., 32.3 parts of a 1:2 mixture by weight of propylene imineand water was added over a period of 45 minutes to iminate carboxylgroups on the first formed acrylic polymer to form pendant amine groups.At the end of the feed the mixture was cooled and stirred at roomtemperature for 16 hours. The Tg of the soft, second formed acrylicpolymer was 0° C. The resulting aqueous polymer emulsion had a solidscontent of 37.1%. The system is crosslinkable on coating formationaccording to one or (most likely) both of embodiments Y and Z. Viaembodiment Y, the crosslinking proceeds by reaction of the amino groupson the first formed acrylic polymer with the carbonyl groups on thesecond formed acrylic polymer. Via embodiment Z, the crosslinkingproceeds by reaction of the amino groups on the first formed acrylicpolymer with the unsaturated bonds of a subsequently added radiationcurable polymer according to component (2) (see later) (Michaeladdition).

Preparation of a Crosslinkable Aqueous Emulsion of an Acrylic PolymerCombination Containing no External Crosslinking Agent (AP7)

A combination of hard acrylic polymer bearing amino and carbonyl groupsand a soft acrylic polymer bearing carbonyl groups was prepared using asequential polymerisation process as follows.

To a round-bottomed flask equipped with a condenser, thermometer andmechanical stirrer, 993.3 parts of water and 8.3 parts of SurfageneFAZ109V were charged. This mixture was heated to 85° C. At 50° C., 10%of a monomer feed consisting of 110.9 parts of water, 270.5 parts ofmethyl methacrylate, 29.5 parts of diacetone acrylamide, 24.4 parts ofmethacrylic acid, 44.6 parts of ethyl acrylate and 24.9 parts ofSurfagene FAZ109V was added. At 75° C., 30% of a catalyst feedconsisting of 1.6 parts of ammonium persulphate and 30.1 parts of waterwas added. As soon as the reaction temperature had been reached theremainders of the monomer feed and catalyst feed were added over aperiod of 60 minutes. At the end of the monomer feed the feed tank wasrinsed with 10.9 parts of water, which was subsequently added to thereactor. The polymerisation mixture was kept at 85° C. for 60 minutesbefore starting the second monomer and catalyst feeds. These consistedof 1.2 parts of water, 273.6 parts of n-butyl methacrylate, 84.4 partsof n-butyl acrylate and 11.1 parts of diacetone acrylamide for themonomer feed and 1.6 parts of ammonium persulphate and 30.1 parts ofwater for the catalyst feed, respectively. Next the mixture was kept atpolymerisation temperature for 30 minutes. Free monomer was furtherreduced by adding a mixture of 0.7 parts of iso-ascorbic acid and 14.0parts of water followed by a mixture of 0.9 parts of an 80 weight-%solution of t-butyl hydroperoxide in water and 1.5 parts of water. Themixture was cooled to 55° C. after which 33.7 parts of a 1:2 mixture ofpropylene imine and water was added to the reactor over a period of 45minutes to iminate carboxyl groups on the first formed acrylic polymerto form pendant amino groups. At the end of the feed the mixture wascooled and stirred at room temperature for 16 hours. The resultingemulsion had a solids content of 37.8% and a pH of 9.2. The Tg of thefirst formed acrylic polymer was 85° C., that of the second formedacrylic polymer was 0° C. The system is crosslinkable on coatingformation according to one or (most likely) both of embodiment Y and Z.Via embodiment Y, the crosslinking proceeds by reaction of the aminogroups on the first formed acrylic polymer with carbonyl groups on thefirst and second formed acrylic polymer. Via embodiment Z, thecrosslinking proceeds by reaction of the amino groups on the firstformed acrylic polymer with the unsaturated bonds of a subsequentlyadded radiation curable polymer according to component (2) (see later)(Michael addition).

Preparation of a Crosslinkable Aqueous Emulsion of an Acrylic PolymerCombination Containing no External Crosslinking Agent (AP8)

A combination of a hard acrylic polymer bearing amino groups and a softacrylic polymer was prepared as follows.

To a round-bottomed flask equipped with a condenser, thermometer andmechanical stirrer, 0.8 parts of ammonium persulphate, and 549.4 partsof the aqueous emulsion of the first formed hard acrylic polymer as perAP3 above were added. 10% of a monomer feed consisting of 209.8 parts ofwater, 293.3 parts of n-butyl methacrylate, 80.3 parts of n-butylacrylate, 824.1 parts of the aqueous emulsion of the first formed hardacrylic polymer from AP3 and 0.4 parts of dimethyl ethanol amine wasadded, after which the temperature was raised to 85° C. At 85° C., theremainder of the monomer feed was added to the reactor over a period of90 minutes. At the same time as the monomer feed was started, a catalystfeed consisting of 43.7 parts of water and 1.1 part of ammoniumpersulphate was started, which should take 100 minutes. After thecatalyst feed had been added the temperature was kept at 85° C. for 30minutes after which the reaction mixture was cooled to 55° C. At 55° C.,32.3 parts of a 1:2 mixture by weight of propylene imine and water wasadded over a period of 45 minutes to iminate carboxyl groups on thefirst formed polymer to form pendant amino groups. At the end of thefeed the mixture was cooled and stirred at room temperature for 16hours. The Tg of the second formed acrylic polymer was 0° C. Theresulting polymer emulsion had a solids content of 37.4% and a pH of9.2. The system is crosslinkable on coating formation according toembodiment Z, the amino groups on the first formed acrylic polymerreacting with the unsaturated bonds of a subsequently added radiationcurable polymer according to component (2) (see later) (Michaeladdition).

Preparation of a Crosslinkable Aqueous Emulsion of an Acrylic PolymerCombination Containing an External Crosslinking Agent (AP9)

A combination of a hard acrylic polymer bearing carboxyl groups and asoft acrylic polymer was prepared as follows.

To a round-bottomed flask equipped with a condenser, thermometer andmechanical stirrer, 0.8 parts of ammonium persulphate, and 549.4 partsof the aqueous emulsion of the first formed hard acrylic polymer as perAP3 above were added. 10% of a monomer feed consisting of 209.8 parts ofwater, 293.3 parts of n-butyl methacrylate, 80.3 parts of n-butylacrylate, 824.1 parts of the aqueous emulsion of the first formed hardacrylic polymer of AP3 and 0.4 parts of dimethyl ethanol amine wasadded, after which the temperature was raised to 85° C. At 85° C., theremainder of the monomer feed was added to the reactor over a period of90 minutes. At the same time as the monomer feed was started, a catalystfeed consisting of 43.7 parts of water and 1.1 part of ammoniumpersulphate was started, which should take 100 minutes. After thecatalyst feed had been added the temperature was kept at 85° C. for 30minutes after which the reaction mixture was cooled to 40° C. At 40° C.a mixture of 7.0 parts of water, 3.3 parts of zinc oxide, 4.2 parts ofammonium carbonate and 6.0 parts of a 25% solution of ammonia in waterwas added over a period of 100 minutes. Next 1.7 parts of Akyporox111/400V (non ionic surfactant) was added followed by 1.6 parts of waterand the mixture was cooled to room temperature. The Tg of the secondformed acrylic polymer was 0° C. The resulting emulsion had a solidscontent of 37.4% and a pH of 10. The system is crosslinkable on coatingformation according to embodiment X by virtue of coordinate covalentbond formation resulting from the donation of electron pairs on oxygenatoms of the carboxyl groups of the first formed acrylic polymer toacceptor shells of the Zn cations in the zinc oxide (acting as anexternal crosslinking agent).

Preparation of an Aqueous Dispersion of a Radiation-Curable Polymer (R4)

A self-dispersible uv curable linear sulphonate stabilised polyurethanepolymer in accordance with component (2) of the invention compositionwas prepared as follows.

To a round-bottomed flask equipped with a thermometer and mechanicalstirrer, 228.3 parts of isophorone diisocyanate, 0.7 parts of2,6-di-tert-butyl-4-methylphenol (Ionol CP) and 0.2 parts of tin octoatewere added and the mixture was heated to 95° C. under a dry airatmosphere. Then 32.8 parts of 2-hydroxyethyl acrylate was added slowlyover a period of 1 hour while the temperature was kept at 95° C. Afterthe complete addition of 2-hydroxyethyl acrylate, the temperature of thereaction mixture was kept at 95° C. for an additional hour. Aftercooling to 50° C., 45.9 parts of methoxypolyethylene glycol (Mw=750;BASF, Germany), 349.2 parts of a sulphonate-functional polyester diolS-1132-110 (OH number=110 mg KOH/g; Occidental Chemical, Belgium), 93.8parts of ethoxylated trimethylolpropane triacrylate (Sartomer SR-454,Sartomer, USA), 0.7 parts of 2,6-di-tert-butyl-4-methylphenol (Ionol CP)and 0.1 parts of tin octoate were added and the mixture was slowlyheated to 95° C. The mixture was held at this temperature until the NCOcontent was 5.12%. 500 parts of this mixture were dispersed into 941parts of water during 1 hour to form an aqueous dispersion of theNCO-terminated prepolymer. Thereafter 14.4 parts of hydrazine were addedas a 64.5% solution in water to chain-extend the prepolymer. Theresulting translucent polyurethane dispersion had a solids content of35% and a pH of 8.0. The unsaturated bond functionality was 1.25 mmolesC=C/g polymer.

EXAMPLES C7, 8, 9, 10, 11, 12 AND 13

Aqueous polymer compositions were prepared by slowly adding theuv-curable urethane dispersion R4 to the acrylic polymer emulsions AP3,AP4, AP5, AP6, AP7, AP8 and AP9 (all solid to solid weight ratio's of3:1, acrylic:urethane) as shown in the following Table 2. Examples 8through 13 are according to the invention while Example C7 iscomparative (the acrylic polymer combination of AP3 having no externalcrosslinking agent for crosslinking the carboxyl groups thereof).

To the blends were added 3% by weight on solids content of a UVinitiator (KIP 100F ex. Lamberti) and the mixtures were allowed to standfor 16 hours before application. Films were subsequently cast with awire rod on test charts to a wet-film thickness of 125 micrometers andalso cast with a film applicator to a thickness of 80 micrometers onglass plates. Drying was carried out rapidly at 60° C. and the coatedtest charts and glass plates were passed twice under a high pressuremercury lamp (120 watts/cm, wave length 240 nm) at 10 m/minutes. Thiseffected UV curing, with covalent crosslinking also having taken placeat ambient temperature after drying (except in Example C7) by reactionof crosslinker groups on the acrylic polymer(s) and with an addedcrosslinker agent (embodiment X) or with other groups also on acrylicpolymer(s) (embodiment Y) or with unsaturated groups on the radiationcurable R4 (embodiment Z).

Xylene rub tests (being a measure of the resistance of the coating toxylene solvent) were performed (both before uv application and after uvapplication) on the coated glass plates using cotton wool soaked withxylene which was rubbed over the surface of the coating, the number ofrubs before failure being listed.

Resistance to blocking (normal blocking only and after uv cure only) wascarried out as described in Examples 1 to C6

The results of the above testing are shown in Table 2.

EXAMPLE 14

An aqueous composition according to the invention was prepared by firstblending the acrylic polymer emulsion AP3 with the UV curablesulphonate-stabilised urethane dispersion R4 (3:1 solids to solidsweight ratio acrylic:urethane) and formulated as described above. Next,to 100 parts of the formulated blend were added 0.7 parts of theaziridine-functional external crosslinking agent Crosslinker CX-100 (ex.NeoResins) which is able to react with carboxylic acid groups on theacrylic polymer backbone (but not with the sulphonate groups on thepolyurethane) and thus induce covalent crosslinking (embodiment X).Films were cast after addition of CX-100 and evaluated as describedabove (in Examples C7, 8 to 13). The results are shown in Table 2.

EXAMPLE 15

An aqueous composition according to the invention was prepared by firstblending the acrylic polymer emulsion AP3 with the UV curable urethanedispersion R1 containing carboxylic acid groups (for stabilisation) (3:1solids to solids weight ratio acrylic:urethane) and formulated asdescribed above. Next, to 100 parts of the formulated blend were added0.7 parts of Crosslinker CX-100™ (ex. NeoResins) which is able to reactwith carboxylic acid groups on both the acrylic polymer backbone and theurethane polymer, thus inducing covalent crosslinking without affectingthe unsaturated double bonds of the polyurethane (embodiment Q). Filmswere cast after addition of Crosslinker CX-100™ and evaluated asdescribed above (in Examples C7, 8 to 13), the results being shown inTable 2.

TABLE 2 Normal Embodi- Xylene rubs Block- Acrylic UV-curable ment beforeafter ing Ex. Component polyurethane of uv uv after uv No. Emulsiondispersion Invention cure cure cure C7 AP3 R4 — 14 30 3  8 AP4 R4 X76 >100 4  9 AP5 R4 X 50 >100 5 10 AP6 R4 Y & Z 52 64 4 11 AP7 R4 Y & Z10 >100 4-5 12 AP8 R4 Z 28 64 4 13 AP9 R4 X 20 60 4-5 14  AP3* R4 X 2440 4-5 15  AP3* R1 Q 40 66 4-5 *plus post added aziridine functionalcrosslinking agent.

EXAMPLES 16 AND 17

These examples are repeats of Example 8 (which uses embodiment X) exceptthat the weight ratios of acrylic:urethane (solids:solids) are changedfrom 3:1 (in Example 8) to 9:1 (Example 16) and 1:1 (Example 17).Formulation and application went identical to the examples of C7, 8 to15. The results (including those for Example 8) are shown in thefollowing Table 3.

TABLE 3 Normal Ratio Xylene rubs Block- Acrylic UV poly- before aftering Ex. Component urethane acrylic:poly- uv uv after uv No. emulsiondispersion urethane cure cure cure 16 AP4 R4 9:1 32  52 2  8 AP4 R4 3:176 >100 4 17 AP4 R4 1:1 14 >100 4

Preparation of an Aqueous Dispersion of a Non-UV Curable Polymer (NR1)

The intention here was to prepare a self-dispersible non-uv curablepolymer (i.e. not in accordance with component (2) of the invention) inorder to prepare a blend of it with the acrylic emulsion AP4 (seeExample C18 following) and to compare this with Example 8 (blend of AP4with the uv-curable polyurethane R4).

A self-dispersible non-uv curable linear carboxylate anion stabilisedpolyurethane polymer, was prepared as follows.

To a round-bottomed flask equipped with a thermometer and mechanicalstirrer, 304.7 parts of isophorone diisocyanate, 40.0 parts ofdimethylol propionic acid (DMPA), 455.3 parts of polypropylene glycolmixture (Voranol; OH number=76.6 mg KOH/g; Dow Benelux, The Netherlands)and 0.15 parts of tin octoate were added and the mixture was slowlyheated to 95° C. under a dry air atmosphere. The mixture was held atthis temperature until the NCO content was 7.59%. Subsequently 24.79parts of triethylamine were added to the reaction mixture. 650 parts ofthis mixture were dispersed into a mixture of 1040 parts of watercontaining 16 parts of a nonyl phenol ethoxylate (Igepal CO-630; Rhodia,Belgium) during 1 hour to form an aqueous dispersion of theNCO-terminated prepolymer. Thereafter 26.5 parts of hydrazine were addedas a 64.5% solution in water to chain-extend the prepolymer. Theresulting translucent polyurethane dispersion had a solids content of38.6% and a pH of 7.3. The unsaturated bond functionality was 0 mmolesC=C/g polymer.

EXAMPLE C18

A blend of AP4 with the non-uv curable polyurethane dispersion NR1 wasprepared at a solids:solids ratio of acrylic:polyurethane 3:1 (Example18). This was compared with Example 8, a blend of AP4 with theself-dispersible uv-curable polyurethane dispersion R4 (acrylic:urethanesolids to solids 3:1), the results being shown in the following Table 4.

TABLE 4 Normal Acrylic Xylene rubs Blocking Component Urethane before uvafter uv after uv Ex. No. emulsion dispersion cure cure cure 8 AP4 R476 >100 4 C18 AP4 NR1 50 — 3

The above results show the improved preparation achieved by the presenceof the uv-curable component (2) in the invention composition.

Preparation of a Crosslinkable Aqueous Emulsion of an Acrylic PolymerCombination Containing an External Crosslinking Agent but Having a TgDifference of 1° C. Between the Polymers A and B (AP10)

A combination of two carbonyl functional acrylic polymers having a Tgdifference of 1° C. between the first and second formed polymers wasprepared using a sequential polymerisation process as follows.

To a round-bottomed flask equipped with a condenser, thermometer andmechanical stirrer, 910.8 parts of water, 1 part of sodium bicarbonate,and 3.1 parts of Surfagene FAZ109V were charged. This mixture was heatedto 85° C. At 75° C., 5% of a monomer feed consisting of 216.9 parts ofwater, 139.0 parts of methyl methacrylate, 39.6 parts of diacetoneacrylamide, 32.7 parts of methacrylic acid, 283.5 parts of ethylacrylate, 9.3 parts of Surfagene FAZ109V, 0.5 parts of sodiumbicarbonate, and 22.3 parts of lauryl mercaptane was added. At 80° C.,30% of a catalyst feed consisting of 1.5 parts of ammonium persulphateand 97.5 parts of water was added. 5 minutes after the temperature hadreached 85° C. a start was made with the addition of the remainders ofthe monomer and catalyst feeds. The monomer feed was added over a periodof 60 minutes, while the catalyst feed was added over a period of 70minutes. At the end of the addition of the catalyst feed 39.2 parts ofwater were used to rinse the feed tank and were added to the reactor. Atemperature of 85° C. was maintained for 30 minutes after which thereaction mixture was cooled to 80° C. At 80° C., the emulsion wasneutralised using a mixture of 56.6 parts of a 25% solution of ammoniain water and 56.6 parts of water. The reaction mixture was subsequentlykept at 80° C. for another 30 minutes before it was cooled to roomtemperature. The resulting acrylic polymer emulsion had a solids contentof 27.2%. The Tg of this first formed acrylic polymer was 21° C.

To a round-bottomed flask equipped with a condenser, thermometer andmechanical stirrer 0.7 parts of ammonium persulphate, and 533.3 parts ofthe aqueous emulsion of the acrylic polymer formed as above were added.10% of a monomer feed consisting of 213.4 parts of water, 351.8 parts ofn-butyl methacrylate, 10.9 parts of diacetone acrylamide, 800.0 parts ofthe aqueous emulsion of the acrylic polymer formed as above and 0.4parts of dimethyl ethanol amine was added after which the temperaturewas raised to 85° C. At 85° C. the remainder of the monomer feed wasadded to the reactor over a period of 90 minutes. At the same time themonomer feed was started, a catalyst feed consisting of 42.4 parts ofwater and 1.1 part of ammonium persulphate was started, which shouldtake 100 minutes. After the catalyst feed had been added the temperaturewas kept at 85° C. for 30 minutes after which the reaction mixture wascooled to room temperature. At room temperature a solution of 19.8 partsof adipic dihydrazide and 11.6 parts of water was added. The Tg of thesecond formed acrylic polymer was 20° C. The polymer emulsion had asolids content of 37.8%. The system is crosslinkable on coatingformation according to embodiment X.

EXAMPLE C19

A blend of the above-prepared acrylic polymer emulsion AP10 with theuv-curable polyurethane dispersion R4 was prepared at a solids:solidsratio acrylic:polyurethane of 3:1 (Example C19). This was compared withExample 8, a blend of AP4 with R4 (acrylic: polyurethane solids:solidsalso 3:1).

Blends and formulations were prepared as described above (in ExamplesC7, 8 to 13). Results are shown in the following Table 5.

TABLE 5 Tg of acrylic Acrylic polymers uv-curable Hardness Xylene rubsNormal Component polymer polymer polyurethane before after before afterBlocking Ex. No. emulsion A B dispersion uv cure uv cure uv cure uv cureafter uv cure 8 AP4  21° C. 85° C. R4 113 s 119 s 76 >100 4 C19 AP10 21°C. 20° C. R4  55 s  67 s 26 >100 0

It is apparent that properties such as surface hardness, blocking andpre-uv cure xylene resistance benefited from a large difference in Tgbetween polymer A and polymer B.

EXAMPLES 20 AND 21

The purpose of these examples was to vary the concentration ofunsaturated double bonds in the polymer of component (2). Example 20 isa blend of the acrylic polymer emulsion AP4 with the self dispersibleuv-curable polyurethane dispersion R1 having an unsaturated bondfunctionality of 0.57 mmoles/g, while Example 21 is a blend of AP4 withself-dispersible commercially available sulphonate-stabilised uv-curablepolyurethane dispersion “NeoRad” R-441 (NeoResins, The Netherlands)(denoted R5 herein) having an unsaturated bond functionality of 2.25mmoles C=C/g polymer. These are for comparison with Example 8 which is ablend of AP4 with the self-dispersible uv-curable polyurethanedispersion R4 having an unsaturated double bond functionality of 1.25mmoles/g. (The solids:solids ratio acrylic:polyurethane in each case was3:1). The compositions were formulated as described above (in ExamplesC7, 8 to 13) and the results of testing are shown in the following Table6.

TABLE 6 concentration Acrylic of unsaturated Xylene rubs NormalComponent Urethane double bonds before after Blocking Ex. No. emulsiondispersion (mmoles/g) uv cure uv cure after uv cure 20 AP4 R1 0.5780 >100 5  8 AP4 R4 1.25 76 >100 4 21 AP4 R5 2.25 83 >100 4-5

Preparation of a Crosslinkable Aqueous Dispersion of a Single AcrylicPolymer Containing an External Crosslinking Agent (AP11)

A single carbonyl functional acrylic polymer was prepared as follows.

To a round-bottomed flask equipped with a condenser, thermometer andmechanical stirrer, 709.1 parts of water and 8.2 parts of SurfageneFAZ109V were charged. This mixture was heated to 85° C. At 65° C. 10% ofa monomer feed consisting of 287.4 parts of water, 256.2 parts of methylmethacrylate, 39.0 parts of diacetone acrylamide, 23.1 parts ofmethacrylic acid, 42.2 parts of ethyl acrylate, 272.1 parts of n-butylmethacrylate, 82.9 parts of n-butyl acrylate and 27.6 parts of SurfageneFAZ109V was added. At 75° C., 30% of a catalyst feed consisting of 3.6parts of ammonium persulphate and 68.1 parts of water was added. 5minutes after the temperature had reached 85° C. a start was made withthe addition of the remainders of the monomer and catalyst feeds. Themonomer feed was added over a period of 90 minutes, while the catalystfeed was added over a period of 100 minutes. At the end of the additionof the catalyst feed 100 parts of water were used to rinse the feed tankand were added to the reactor. A temperature of 85° C. was maintainedfor 30 minutes. Next, free monomer level was further reduced by adding0.7 parts of iso-ascorbic acid dissolved in 13.6 parts of water followedby 0.9 parts of an 80 weight % solution of t-butyl hydroperoxide and 1.5parts of water after which the mixture was stirred at 85° C. for another30 minutes. The batch was cooled to room temperature after which pH wasraised to 7.0 by adding 7.6 parts of a 25% solution of ammonia in waterand 7.6 parts of water followed by addition of 20.3 parts of adipic aciddihydrazide. The resulting acrylic polymer emulsion had a solids contentof 37.5% and a Tg of 37.8° C.

EXAMPLE C22

A blend of the single polymer emulsion AP11 with the self dispersibleuv-curable polyurethane dispersion R4 was formed (Example C22). Thepurpose of making this was for comparison with Example 8 which is thehard and soft two polymer combination acrylic emulsion with R4 (bothhaving a solids:solids acrylic:urethane ratio of 3:1). The blends wereformulated and tested as described above (in Examples C7, 8 to 13). Thetest results are shown in the following Table 7.

TABLE 7 Xylene rubs Normal before after Blocking Ex. Acrylic UrethaneType of uv uv after uv No. emulsion dispersion emulsion cure cure cure 8AP4  R4 two polymer 76 >100 4 combination C22 AP11 R4 single 66 >100 0polymer

The results clearly show that blocking properties are completely lostwhen using the single polymer arylic polymer.

What is claimed is:
 1. Aqueous polymer composition suitable for coatingwhich comprises the following components dispersed in water: (1) acombination of an acrylic polymer(s) A and an acrylic polymer(s) B wherepolymer(s) A has a Tg of not more than 30° C. and polymer(s) B has a Tgof at least 35° C., which is at least 25° higher than the Tg ofpolymer(s) A, and wherein one or both of polymers A and B bearcrosslinker functional groups capable of imparting ambient-temperaturecrosslinkability to component (1) in a coating formed from thecomposition via the formation of non-radically-formed covalent bonds;and (2) a self-dispersible, ionically stabilised polymer havingolefinically unsaturated bond functionality capable of impartingradiation-curability thereto in a coating formed from the composition.2. Composition according to claim 1 wherein one or both of polymers Aand B of component (1) bear crosslinker functional groups for reactionwith an already present or subsequently added external cross-linkingagent having 2 or more groups which are reactable with the crosslinkergroups on one or both of polymers A and B to form crosslinking covalentbonds (Embodiment X).
 3. Composition according to claim 2 wherein thecrosslinker functional groups on one or both of polymers A and B arecarbonyl groups and the groups of the external crosslinking agentreactable therewith are carbonyl-reactive amino groups.
 4. Compositionaccording to claim 3 wherein said carbonyl-reactive amino groups areprovided by —NH₂ or —NH— groups which are bound only to a carbonatom(s), or carbonyl-reactive groups derived therefrom.
 5. Compositionaccording to claim 3 wherein said carbonyl-reactive amino groups areprovided by hydrazine functional groups or carbonyl-reactive groupsderived therefrom.
 6. Composition according to claim 2 wherein thecrosslinker functional groups on one or both of polymers A and B arecarboxyl groups and the groups of the external crosslinking agentreactable therewith are selected from aziridine, carbodiimide,cycloaliphatic polyepoxide and epoxy silane groups.
 7. Compositionaccording to claim 1 wherein one or both of polymers A and B ofcomponent (1) bear crosslinker groups capable of donating lone pairs ofelectrons to acceptor shells of metal ions of an already present orsubsequently added metal compound, acting as an external crosslinkingagent, thereby forming coordinate crosslinking bonds (Embodiment X). 8.Composition according to claim 7 wherein said crosslinker groups arecarboxyl groups and the metal ions are zinc ions.
 9. Compositionaccording to claim 1 wherein each of polymers A and B of component (1)bear different crosslinker functional groups which are reactable witheach other (co-reactable) to form crosslinking covalent bonds(Embodiment Y).
 10. Composition according to claim 9 wherein theco-reactable groups are carbonyl groups and carbonyl-reactive aminogroups.
 11. Composition according to claim 10 wherein thecarbonyl-reactive amino groups are provided by amino ester groups. 12.Composition according to claim 1 wherein one or both of the acrylicpolymers A and B of component (1) bear crosslinker functional groupswhich are reactable to form non-radically formed covalent crosslinkingbonds with the olefinically unsaturated bonds of the polymer ofcomponent (2) (Embodiment Z).
 13. Composition according to claim 12wherein the crosslinker functional groups on one or both of acrylicpolymers A and B of component (1) are primary or secondary amino groups.14. Composition according to claim 13 wherein said amino groups areprovided by amino ester groups.
 15. Composition according to claim 1wherein one or both of polymers (A) and (B) bear crosslinker groups, andthe radiation-curable polymer of component (2) also bears crosslinkergroups, these not being the olefinically unsaturated bonds of thepolymer of component (2), said crosslinker groups being for reactionwith an already present or subsequently added external crosslinkingagent having 2 or more groups which are reactable with said crosslinkergroups on polymer (A) and/or (B) and on the polymer of component (2) toform crosslinking covalent bonds (Embodiment Q).
 16. Compositionaccording to claim 15 wherein the crosslinker groups on one or both ofpolymer (A) and (B) and on the polymers of component (2) are carboxylgroups, and the groups of the external crosslinking agent reactivetherewith are aziridine groups or metal ions.
 17. Composition accordingto claim 1 wherein said radiation-curable polymer of component (2) hasan olefinically unsaturated bond functionally of at least 0.25 mmolesC=C/gram polymer.
 18. Composition according to claim 1 wherein the ionicstabilisation of said radiation-curable polymer of component (2) isprovided by internal anionic dispersing groups.
 19. Compositionaccording to claim 18 wherein said polymer of component (2) additionallyhas nonionic internal dispersing groups.
 20. Composition according toclaim 1 wherein said radiation-curable polymer of component (2) is auv-curable polyurethane.
 21. Composition according to claim 20 whereinthe olefinically unsaturated bonds of the polymer of component (2) areprovided by an acryloyl or methacryloyl functional monool or polyolemployed in the urethane synthesis.
 22. Composition according to eitherclaim 20 or claim 21 wherein the ionic stabilisation of saidpolyurethane is provided by employing in the synthesis thereof adihydroxy alkanoic acid of formula:

wherein R⁴ is H or alkyl.
 23. Composition according to claim 20 whereinsaid polyurethane is the chain-extended reaction product of an aqueousdispersed isocyanate-terminated urethane prepolymer and an activehydrogen chain-extending compound.
 24. Composition according to claim 1wherein the acrylic polymers A and B of component (1) have been formedby a sequential polymerisation procedure.
 25. Composition according toclaim 1 wherein polymer B of component (1) has a Tg which is at least40° C. higher than that of polymer A.
 26. Composition according to claim1 wherein the weight ratio of polymer A to polymer B in component (1) iswithin the range of from 30/70 to 90/10.
 27. Composition according toclaim 1 wherein the weight ratio of the polymers of component (1) to thepolymer of component (2) is within the range of from 20/80 to 97/3. 28.Method of coating a substrate using an aqueous composition according toclaim
 1. 29. Method according to claim 28 wherein the substrate is wood.30. Method according to claim 29 wherein the substrate is provided by adoor or window frame.
 31. Coating obtainable or derived from an aqueouscomposition according to claim
 1. 32. Substrate having a coatingobtainable or derived from an aqueous composition according to claim 1.33. Composition according to claim 1 wherein said radiation-curabilityof the polymer (2) is uv-radiation curability.
 34. Composition accordingto claim 1 wherein polymer(s) B has a Tg of at least 45° C. 35.Composition according to claim 5 wherein the hydrazine functional groupsare part of acid hydrazide groups or semi-carbazide groups. 36.Composition according to claim 11 or 14 wherein said amino ester groupsare derived by iminating a precursor polymer bearing carboxyl groups.37. Composition according to claim 15 wherein the crosslinker groups ofthe radiation curable polymer of component (2) are the same as those ofat least one of polymer A and polymer B.
 38. Composition according toclaim 17 wherein the olefinically unsaturated bond functionality of saidradiation curable polymer of component (2) is 0.5 to 3 mmoles C═C/grampolymer.
 39. Composition according to claim 18 wherein said internalanionic dispersing groups are carboxylate anion groups or sulphonateanion groups.
 40. Composition according to claim 22 wherein saiddihydroxyalkanoic acid is 2,2-dimethylol propionic acid.
 41. Compositionaccording to claim 25 wherein polymer B of component (1) has a Tg whichis at least 50° C. higher than that of polymer A.
 42. Compositionaccording to claim 26 wherein the weight ratio of polymer A to polymer Bis within the range of 40/60 to 80/20.
 43. Composition according toclaim 27 wherein the weight ratio of the polymers of component (1) tothe polymer of component (2) is within the range of 45/55 to 90/10.